Throughout the 1980s and 1990s the heavy-duty truck market exploded as Dodge began implementing the use of Cummins engines and Ford continued to develop their IDI engines. By 1994, Dodge was seeing redesigned their trucks and saw massive success and by 1999, Ford had released their all new Super Duty F-series trucks.
While Ford was enjoying also enjoying massive new success with their new platform and impressive 7.3L Powerstroke engine they introduced earlier in the 90s, GM was hard at work developing a new platform, an entirely new truck with a new drivetrain and engine with the hopes of blowing the doors off of both Dodge and Ford.
And that’s exactly what they did in the coming years.
Not only did GM develop the first direct competitor to Ford’s new Super Duty line of trucks, their new trucks also brought loads of new developments to the heavy-duty truck market that we hadn’t previously seen.
With that in mind, let’s rewind the clock and really take a deep look at how GM changed their heavy-duty trucks throughout the years and kept up with Dodge and Ford’s trucks.
And to preface this article, we should mention we’re not talking about anything like the GMC General or any “true” heavy duty vehicles that GM has built. That being said, “heavy duty” GM trucks have been around for a long time, depending how you want to define heavy-duty and how far back you want to go.
The Start of it All in 1973
If you consider anything past a 1/2 ton truck as heavy duty, then the 1918 Chevrolet One-Ton is the starting point of it all. But, for this article we’re going to start the story in 1973 when Chevy introduced the C30 one-ton Dually crew cab truck.
At the time, this was the first ever crew-cab Dually on the market and realistically, it’s one the first ever modern heavy duty trucks.
Not only was this new C30 truck an absolute unit with capabilities never before seen in modern heavy-duty truck, but it also came packaged in the square body design that we all know and love.
The even crazier part? The MSRP for this model in 1973 was a whopping $4,388, which translates to $29,452 in today’s dollars, which kind of puts into perspective the insane value that GM was offering with this truck.
Unfortunately, this was well before diesel engines became popular in heavy-duty trucks, so the C30 was stuck with the rather underwhelming 350-cubic inch V8 engine with an insane, earth shattering 155 horsepower and 255 lb.-ft. of torque. Luckily, later down the line of the square body lineage, more powerful engines such as the 454ci V8 became available.
What’s even more important to the story, to the history of GM’s heavy duty trucks, is that in 1982 we saw the introduction of the 6.2L diesel. While it’s pretty hard to make a case for the 6.2L diesel being anything other than a turd or a boat anchor, it laid the groundwork for the better diesel engines to be introduced later on.
Revamped in 1988
Jumping up to 1988, we saw the fourth generation of the C/K truck introduced and this time around it came with a much more modern look on the all new GMT400 platform. However, this new platform came in a few different forms.
For example, the 1991 and onwards C3500 were on the GM455 chassis, the Suburban was either on the 410 or 425 chassis, and so on.
This is also where we saw the introduction of a much better diesel engine, the 6.5L diesel.
This engine was introduced in 1992 and was available in both naturally aspirated and turbocharged variants. That being said, the entire lifespan of the 6.5L diesel was pretty much just trying to keep up with what Ford and Dodge were offering with their respective diesel powered trucks.
With that in mind, the OBS generation of GM truck was pretty short lived from 1988 to 1998, as in 1999 the all new platform was introduced and it was miles ahead of anything GM had ever offered with their trucks.
Part 1: 1999 to 2007
With the new generation of GM trucks in 1999 came a complete redesign which finally brought their trucks into the modern age. The platform is was all based on? The GMT800.
For the heavy duty trucks, this a three-piece frame system that features a hydroformed front section, a roll-formed or stamped mid-section and a stamped rear C channel section.
The Hydroformed tubular crossmembers and close-out plates helped provide improved torsional rigidity which in-turn, helps the truck haul and tow much better and safer. The only real unfortunate downside, is that while Ford and Dodge continued to offer their heavy-duty trucks with a solid front axle, GMT800 frame was designed around independent front suspension.
Of course, the previous GMT400 chassis was also independent suspension in the front, but it’s not something you really love to see in heavy duty applications, as a solid front axle is plain and simple a stronger and simpler solution.
In the rear of the GMT800 chassis we saw leaf spring rear suspension and two engine options from 1999 to 2001: the 6.0L Vortec V8 and the 8.1L big-block Vortec V8.
Where things really got interesting with GM’s new heavy duty trucks is in 2001 when we saw the introduction of the new 6.6L LB7 Duramax V8 turbo-diesel.
We’ve covered the history of the Duramax engine in depth in another article which I highly recommend you check out, but as a quick refresher, this new Duramax diesel engine was a result of a collaboration between GM and Isuzu and it offered loads of new features never seen in the pickup truck market.
Some of these features include the new common-rail injection system supplied by Bosch, aluminum cylinder heads rather than cast-iron heads, and it was the first diesel engine in this segment to reach 300hp. The LB7 engine had a relatively short life from 2001-2004, which was followed by the LLY Duramax and then the LBZ Duramax.
But, as I mentioned earlier, this new generation of GM trucks had tons of things we had never seen in this segment. As if the new Duramax diesel with class-leading horsepower and torque at the time wasn’t enough, then took it even further by putting an insanely tough, strong, and reliable transmission behind it, which is Allison 1000.
Part of what the new 1000 series Allison transmissions so special as compared to the Ford 4R100 or the Dodge 47RE, is that the Allison transmission was a five-speed rather than a 4-speed. It also featured state-of-the-art electronic controls with adaptive learning and a Tow/Haul mode that was way ahead of anything anyone else was offering at the time.
By 2006 the Allison 1000 was upgraded even further into a six-speed version which also coincided with the new the LBZ Duramax in the same year.
And while I mentioned my distaste for independent front suspension on heavy-duty trucks, the AAM 9.25 IFS system on the GMT800 platform isn’t half bad. The 9.25 refers to the different ring gear diameter, and outside the diff the whole system is comprised of strong half-shafts, weight-saving control arms, and torsion bars to suspend the whole thing.
Out back, we have the AAM 1150, which was first found in GM’s truck in 2001. This is a massive and borderline overkill rear axle with an 11.5″ ring gear diameter, which was larger than any other 3/4 ton axle at the time. Funny enough, Dodge began offering a very similar AAM 1150 rear axle in their heavy duty Ram trucks beginning in 2003.
While this generation of GM truck had its time in the sun and competed very well with Ford and Dodge trucks, often outdoing them in specific performance measurements, by 2007/2008 it was time for them to introduce a new body style to keep up with the modern times.
Part 2: 2008 to 2011
GM introducing a new body style to their heavy duty truck wasn’t just for show either. Dodge updated their trucks and added common rail injection in 2003 and Ford revamped their SuperDuty trucks in 2005 with coil spring suspension and improved towing capacities. If GM wanted to stay on top, it was going to take a big change, which is is exactly what they delivered.
In terms of body styling, the outgoing 2007 trucks looked nothing like the new 2008 truck. The big show piece? The new front-end with bigger headlights, and really bigger everything. Of course, it’s worth noting that the front end on these new 2008 heavy duty trucks was very much based on the half-ton trucks that debuted their new body style in 2007.
And yes, for the die-hard GM fans out there, it was technically 2007.5, but that technicality isn’t important at all. As per Chevy, the HD Silverado had been treated to “bold, muscular designs that are differentiated from their light-duty siblings.”
The treatments they’re referring to include a wider and taller grille, large, reflector-optic headlamps, domed hoods and flared front fenders intended to enhance the truck’s wide stance. Realistically though, the majority of people out there can’t even tell if a 2008 truck is a 1500 or a 2500 from the front-end, so a lot of this was more or less just marketing.
With the new body also came a new chassis upon which it sat, the GMT900. The exact same AAM 9.25 IFS system we mentioned earlier was retained, but the frame was improved. More specifically, the mid-section featured a lipped C-channel. Up front the frame was hydroformed and the rear was c-Channel.
Really, this new frame and suspension is more or less simply an evolution of the outgoing GMT800 chassis, rather than an entirely new platform, which is fine considering there was nothing particularly wrong with the previous chassis.
Under the new body and bolted to the new evolved Chassis was a new and improved powertrain, and at the heart of it all was the new LMM Duramax. Upon initial launch in 2008, this new engine delivered 365 and 660lb-ft of torque, which was best-in-class for the time.
As compared to the outgoing LBZ Duramax, the LMM Duramax used revised injector nozzles, an EDC16 Bosch ECM with new emissions-related internals and revised cylinder head water passages for enhanced cooling.
On the the gasoline side of the heavy duty line of trucks, the VortecMAX 6.0L V8, saw horsepower increase to 353 hp and 373 lb-ft of torque.
The Allison transmission remained and rightfully so. This time around though, it offered an increased torque input capacity which was simply required as a function of the LMM’s increased power output. And whether or not you enjoy these types of systems, this was the first time we saw GM offer a factory-integrated trailer brake controller in their heavy-duty trucks.
I know for a lot of guys and gals out there that tow a lot, an aftermarket unit is often still preferred to a factory integrated unit, but the point is that GM was adding things left and right with their new trucks in 2008 in order to try to keep up with or beat out the competition.
The unfortunate downside with the new LMM Duramax was the addition of some new emissions components, particularly the diesel particulate filter and a larger EGR cooler. We won’t go into the cons of these emissions systems on diesel engines in this article, as we’ve already done that with our Duramax guide article.
Of course, you have to remember the 2008 trucks were released during a bad time economically, and then later a 4-month pause in Duramax engine production. Regardless though, the 2009 to 2011 trucks were quite successful. Not as successful as the smaller 1500 trucks from the same time frame, but still well enough for GM to bring more innovations to the market in 2011.
Part 3: 2011 to 2016
And with their new 2011 trucks, the idea was simple: take back the lead in terms of towing capacity, max payload, chassis strength, sheer power output, and they did exactly that for a short time until Ford reflashed the 6.7L Powerstroke up to 400hp and 800lb-ft of torque.
On the outside, however, you wouldn’t be able to tell that there was any change from the 2010 to 2011 heavy duty GM truck models, but underneath were massive improves to the chassis, suspension, engine, and more.
The star of the show, almost as always with GM’s heavy duty truck updates, was the new LML Duramax. With the previous LMM at 365hp and 660lb-ft of torque it was pretty decent in terms of power, but the LML took it way further with a huge jump to 397hp and 765lb-ft of torque.
Part of this was thanks to the improved Bosch injection system, as well as a number of other factors. And not only did it output quite a bit more power, but it also output significantly less emissions. But of course, that’s only a good thing on paper. The reality is that the LML had new parts added to it, namely the selective catalyst reduction system in order to reduce emissions output, which ultimately reduced overall reliability of the engine.
Behind the engine was the same Allison 1000 transmission with six gears, but it was slightly improved with a variable pressure main line to help reduce transmission fluid temperatures, which in turn, improved towing and hauling ability. There was also the addition of a new torque converter, and low-drag clutches for reduced drivetrain loss.
This is also when we saw the new exhaust brake system added to the Duramax powered trucks, and this worked through the variable geometry turbocharger and works hand-in-hand with the tow/haul mode to help slow the truck down on deceleration.
Aside from the improved power output and slightly improved transmission, the big thing that really helped GM’s heavy duty trucks take a massive leap from 2011 onwards was the new fully boxed frame. This was a big improvement over the C-channel frame previously found on the GMT900 heavy duty chassis, but it also added quite a bit of extra weight.
Another area where we saw big improvements in 2011 was the rear suspension, which interestingly enough, now featured an asymmetrical leaf spring setup. This design locates the rear axle forward of the center of the spring pack to help reduce axle wrap.
For those who don’t know, that’s simply when the axle has so much rotational force on it, namely through power and heavy load otherwise the tires would spin, and the leaf spring will start to wrap. This is bad as it reduces the springs ability to effective handle the load, but also dangerous because the spring can violently unwrap and cause wheel hop in certain situations.
There’s other issues with axle wrap, but that’s the gist of it. GM also upgraded the width of the leaf springs from 2.5 inches to 3 inches to further improve rear end stability. But this also meant that these trucks had pretty poor ride quality, even for a 3/4 ton truck.
On the front end suspension, we also saw some changes. Namely larger torsion bars were added, forged-steel upper control arms were used, and cast-iron lower control arms were used. We also saw larger knuckles.
The improved rear suspension, improved front suspension, and fully boxed frame all led to a total weight increase of around 500lbs between the 2010 and 2011 heavy duty trucks.
On the gas side of things, everything was pretty much the same with a very similar 6.0L Vortec being the only option even though the smaller 1500 trucks could be optioned with the 6.2L Vortec.
And while GM’s trucks were visually the same until 2019 when we saw the refresh, in 2017 we saw another very big update to their heavy duty lineup.
Part 4: 2017 to 2023
At this time, Ford and Dodge were pushing to establish themselves as trucks that could pull 30,000lbs. Meanwhile, GM decided not to pursue this insane towing figure in 2017, but rather to improve the overall towing experience and then later down the line in a few years up the towing capacity to numbers that rival or surpass some medium-duty trucks.
The star of the show, once again with a truck update, was the new Duramax engine engine. This time around it was yet another evolution of the 6.6L, this time with the codename L5P. This version features a new high-pressure common rail injection system, new BorgWarner variable turbocharger and much more, all of which led to an at the time class leading 445hp and 910lb-ft of torque.
Behind this new and more powerful Duramax engine was the same Allison 1000 six transmission, however, that soon to change as in 2020 GM introduced an all new Allison transmission, and this time around it was a completely new ten speed design.
The 10L1000 is said to have been fully built by GM but with careful oversight provided by Allison Transmission. So it’s not exactly clear if this is a true Allison transmission or if GM simply kept the Allison name on it for improved marketability. Regardless of the naming convention, the new 2020 model 10-speed transmission has since been proven as an excellent transmission across the board.
Another interesting change the made for the 2017 update was a new GM GMTK2XX platform, which is functionally very similar to the outgoing fully boxed GMT900 platform. And atop the chassis was nearly the same front-end, rear-end, and cab. GM made a big point of out boasting that their trucks used steel when Ford decided to switch to aluminum.
But, in 2019/2020 we saw a huge visual update to all GM trucks, including the heavy duty models which a much taller front end.
As we mentioned a moment ago, the 2017 trucks kept the same towing rating at 23,200lbs, which by itself, is not bad at all. But, in 2020 GM decided to crank it up a massive notch with the 3500HD models coming in with an insane 35,500lb towing rating. This was mainly from the addition of the new 10-speed transmission, as well as larger rear end as compared to earlier trucks.
One year later in 2021, the max towing was increased yet again, this time to 36,000 pounds, which was a best-in-class figure at the time.
While they technically were losing the war on torque output, they managed to finally improve on the gas side of things where we saw the introduction of the new 6.6L L8T engine, which offered much better performance as compared to the 6.0L Vortec previously found in the heavy duty gas trucks.
Summary
And that’s kind of that. We saw the visual update in 2019, but there hasn’t been any massive changes to GM’s heavy duty trucks since then. Keep in mind, we’re shooting this on the tail end of 2022, so we could see some major changes either in 2023 or 2024. Presumably an update to the L5P with more power, maybe improved towing ratings, who knows?