We take GMC’s diesel-drinking half-ton pickup off the beaten path.
The rumors of the diesel engine’s demise are greatly exaggerated. Case in point: the half-ton truck market, where every America brand now offers the option of a diesel engine in its respective entrant. One of the latest additions to this segment is the 2020 GMC Sierra 1500, which shares its available turbodiesel 3.0-liter inline-six with its Chevrolet Silverado 1500 cousin.
As in the Chevy, the 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.
Introduced to compete with the likes of the Ram 1500 Rebel (which is also available with a diesel engine) and the Chevrolet Silverado Trail Boss, the AT4 features a two-inch lift relative to other Sierra 1500 models, Rancho monotube shocks, available Goodyear Wrangler DuraTrac off-road rubber, a slew of underbody skid plates, standard four-wheel-drive, and a locking rear differential. In short, it’s a pickup that offers more off-road chops than the typical half-ton truck, while sacrificing little of the Sierra 1500’s on-road dynamics.
That's the theory, at least. I can't comment on how that pans out in practice, as GMC limits my drive of the AT4 diesel to a small off-road loop located in the town of Alpine, Wyoming, following our test of the Sierra HD. The course starts with a small but tall rock hill that’s designed to show off the ample torque of the engine, which it channels to all four wheels by way of a smooth-shifting 10-speed automatic transmission. With its four-wheel-drive system set to Low, the AT4 diesel crests the hill with surprising ease. That said, the abundance of twist does lead to some unnecessary wheel spin. You'll need a light right foot when taking the AT4 diesel off-road.
The truck's hill-descent control system makes the journey downhill easy. Once on level ground, I guide the truck through a troth of mud, which the Goodyear tires do a fine job of plodding through without showing any signs of unexpected slip.
Finally, I enter a gravel road, which allows me to uncork the diesel engine ever so slightly. However, with speeds barely topping 40 miles per hour, it's hard to determine the powertrain's true accelerative capabilities. That said, little engine noise enters the cabin and the AT4-specific suspension turning results in a surprisingly smooth ride over the dusty road’s varying undulations.
GMC limited my drive of the AT4 diesel to a small off-road loop located in the town of Alpine, Wyoming, following our test of the Sierra HD.
Yet, I exit the Sierra 1500 AT4 diesel with more questions than answers. I still want to know how the engine moves this mighty truck in the real world, as well as if the powertrain's quiet nature at low speeds breaks into an uncouth clatter at higher revs.
What I do know, though, is that the plentiful low-end grunt of the diesel makes it a fine ally off-road and that the truck’s combined fuel economy rating by the Environmental Protection Agency of 24 miles per gallon betters the four-wheel-drive Ford F-150 diesel's 22 MPG figure and the 5.3-liter V8-equipped Sierra 1500 AT4's 18 MPG sum.
The diesel engine is very much alive in the half-ton pickup segment, and its competence off-road is but one of the many reasons for its renewed push by American truck brands. Still, most truck buyers spend their hours driving on tarmac. Although the fuel economy gains of the 2020 GMC Sierra 1500 AT4 diesel certainly give it a leg-up over the model's gas-guzzling alternatives, I still have to wonder if the diesel's charm in day-to-day driving can match that of the truck's available 5.3- or 6.2-liter V8 engines.