The 2020 GMC Sierra Heavy Duty is a bit of a mixed bag. It excels at the tasks an owner is likely to require from a massive pickup truck, but the interior is a definite letdown. Taken as a whole the truck boasts several class-leading specifications and features that make up for the lackluster look and feel of the cabin. And it’s much more successful than the mechanically similar Chevy Silverado HD, which shares the Sierra’s weaknesses but few of its subjective strengths.
GMC’s Sierra HD may share most of its major bits and pieces with the Silverado, but the strongest reason to pick the GMC over the Chevy is that the SLE and SLT trims of the Sierra HD are legitimately handsome. And the rugged, off-road-themed AT4 package is new for 2020 with a blacked-out look that we think a lot of buyers are going to love. Even the ostentatious, chrome-dipped Denali trim looks classy compared to the in-your-face look of Ford’s Super Duty line. The same can’t be said for the Silverado HD, which, depending on trim level, varies from garish to just plain ugly.
GMC’s diesel-drinking straight-six belts out 277 horses and 460 pound-feet of torque, the latter of which tops the truck’s available 5.3-liter V8 engine’s peak torque by 37 lb-ft. While GMC offers the engine on various Sierra 1500 models (SLE, Elevation, SLT, AT4, and Denali), the brand restricts my seat-time with the diesel truck to the off-road-ready AT4 trim.
For those who might not be familiar with the relatively new AT4 off-road package (an evolution of the earlier All Terrain package), it offers quite a few unique features that make it a strong performer in challenging terrain. When paired with the torquey performance of the Duramax engine, we’re guessing this will likely be one of the most popular setups for those who like to explore remote from the northeast to the southwest. In the name of full disclosure, GMC’s AT4 package is effectively the same as the Chevy Silverado 1500 Trail Boss, offering a uniquely tuned 2-inch suspension lift, Rancho monotube shocks, bigger wheels and 32-inch all-terrain tires, extra skid-plating, a G80 auto-locking rear diff, and a few other technology details like surround view cameras, hill descent control, and a color heads-up display that provides forward, back, and side-to-side incline readouts.
Duramax AT4 was driven over a nasty rock-strewn course in low range and found the setup, especially with the forward and surround-view cameras, an easy no-spotter, stress-free ascent. Also available is a feature that detects the steepness of your incline when you take your foot on-then-off the brake and will hold it automatically until you touch the throttle. That hill-hold technology could prevent a lot of body damage. During this section of the test, it was noticed that cameras are only as good as their ability to shed mud and dirty water. It would have been nice to have a quick squirter nozzle (at least on the front and rear lenses) to give us an idea of what to expect when the doors were opened .
Clearly, the off-road portion tested was the most fun, it gave us a chance to let the horses run. We got a pretty good idea that this setup is more than capable of multi-tasking, a particularly important detail for many new-truck buyers. As to how this package (Denali or AT4 Duramax) will hold up against the Ram and Ford offerings, we can’t be exactly sure, given our altitude driving and limited time with the trucks. But we can say GM engineers have done a stellar job seamlessly integrating the engine’s power with the super-smart, selectable 10-speed transmission. We never felt a hard shift or clumsy hunt for the next gear no matter what the situation, which we’ve experienced in both of its competitors.
There’s a new 6.6-liter gasoline V8, too, which is unfortunately still hooked to a six-speed automatic transmission. Its 401 horsepower and 464 pound-feet of torque look impressive on paper — Ford’s current 6.2 spins out 385 hp and 430 lb-ft (a 7.3-liter gasoline V8 is coming for 2020 with what we’d assume will be class-leading power figures), while Ram’s 6.4 offers 410 ponies and 429 lb-ft. Out in the real world, though, all three of these huge behemoths really cry out for their diesel options, as expensive as they may be.
This low-rent interior doesn’t feel quite as galling in a truck wearing a Chevy badge up front, but GMC makes no bones about the fact that it’s targeting a higher class of clientele, focusing particular attention on its Denali (that’s the top-level Denali trim in the images above) and newer AT4 trims. According to GMC, if Denali were broken out into its own badge separate from its parent company, its $54,000 average transaction price. A Sierra Denali 3500 Crew Cab starts at a little over $66,000 but most trucks will cost significantly more.