In addition to a two-speed transfer case, AT4s have hill-descent control, skid plates to protect delicate mechanical components and a special off-road suspension with Rancho shocks. AT4 models are only offered with an extra-spacious crew-cab body, though two bed lengths are available: 82.2 inches and 98.3 inches. Thanks to clever engineering, these boxes promise best-in-class volume, which is ideal for hauling more gravel, firewood or furniture per load. Making it just a touch easier to reach items stored in its towering, shoulder-height bed, the Sierra 2500 features integrated side steps and cutouts in the rear bumper.
Capping that cargo box is an available MultiPro tailgate, one of the most innovative pickup truck features to come out in years. With six different postures, this gate allows you to support loads more easily, it provides a sturdy step into the bed, helps keep different sizes of cargo secure and even functions as a small work surface, a place to set your laptop or clipboard. Ford’s latest tailgates can’t hold a candle to this and even Ram’s innovative Multifunction gate isn’t as useful.
No surprise, there’s nothing groundbreaking under this truck’s soaring hood. Two engines are offered: a gasoline V8 and a proven 6.6-liter Duramax diesel. If you can afford the whopping $9,890 upcharge and have serious work to do, get the optional oil-burner, which comes paired with a 10-speed Allison transmission. This combo is dynamite, hands-down superior to the Sierra HD’s standard engine. In fact, this may be the best heavy-duty truck powertrain in the business. The Duramax delivers 445 horsepower and 910 pound-feet of torque, slightly behind diesel-powered Ford and Ram trucks in the twist department, though the difference is academic. This GMC is still surprisingly quick and the engine super smooth, with no obnoxious vibration or clattering. The transmission’s performance is also perfect. It shifts with luxury-car smoothness and never stumbles.
This diesel-powered Sierra 2500 AT4 can haul up to 3,029 pounds and drag a maximum of 18,500 pounds, either conventionally or with a fifth-wheel/gooseneck trailer. Making towing just a little less stressful are large exterior mirrors that not only feature convex reflectors but extend and fold at the push of a button.
Helping enable this impressive capability, the Sierra features an independent front suspension with torsion bars. Out back is your traditional live axle supported by leaf springs. Predictably, this setup provides a ride that’s fairly stiff, though even unladen it’s not brutal. Throw a few hundred pounds in the bed and things smooth out noticeably. This truck’s recirculating ball steering system is reasonably precise and doesn’t require constant attention to track straight, though the excessively tall, squared-off hood makes it a challenge to place this truck in its lane.
Not to bludgeon a deceased equine, but the Sierra 2500’s interior isn’t great. This truck and its light-duty siblings have limped along for the last few years with cabins that are clearly behind the competition, loaded with hard, unattractive plastics, lackluster leather and middling tech. Luckily, help is on the way — for half-ton versions of the Chevy Silverado and GMC Sierra at least. The updated 2022 models feature dramatically revamped digs, with vastly improved materials and features. GM hasn’t said whether these redecorated interiors will find their way to the heavy-duty line, but it’s a good bet they will, and hopefully in short order.
It’s easy to denigrate the Sierra’s interior, but not everything is bad. The ergonomics, for instance, are solid. This truck’s climate and audio switches are dead simple and the trailer brake controller is clearly visible and easy to reach, located near the bottom of the center stack. If the load you’re dragging starts to get a little frisky, you’ll be glad this isn’t hard to find. I also love the old-school column-mounted shifter. It’s more tactile and satisfying than a dial or buttons.
The Sierra 2500’s elevated ride height provides vista-like views of surrounding traffic, though comfort is hit or miss. The front bucket seats are firm and flat, with little bolstering and even less contouring. The rear accommodations in this crew-cab model are similar, though there is a ton of space for passengers with real stretch-out legroom. For added versatility, that split rear cushion lifts, revealing additional storage nooks or allowing you to carry bulky cargo. Ingeniously, the rear seat backrests have hidden storage cubbies as well, which are a great place to stash smaller items away from prying eyes.
Along with comfort, tech is a mixed bag in this rig. The available 8-inch infotainment screen with embedded navigation looks tiny on such a huge dashboard. The display’s viewing angles are also mediocre, with everything looking washed out from the driver’s seat. But hey, at least GMC nailed the infotainment system. It’s super responsive, easy as pie to navigate and the crisp icons look great. Beyond that, Android Auto and Apple CarPlay are supported and both smartphone-mirroring systems can connect wirelessly.
A bunch of must-have goodies are bundled in the $7,975 AT4 Premium Plus Package. This pricey options group includes a wireless phone charger, power sliding rear window and Bose sound system. Advanced driver aids like rear cross-traffic alert, lane-departure warning, a rear camera mirror and automatic high beams are included, too — features that, if not mandatory in a hulking vehicle like this, sure are nice to have.
Among other things, the AT4 Premium Plus Package also comes with GM’s excellent HD Surround Vision 360-degree camera system, which provides up to 15 views and is a godsend when parking or hooking up a trailer. A Safety Alert seat is included, too, which buzzes your butt to warn of a possible forward collision or if you cross a lane marker.
Matching its size and weight is this Sierra’s price. As tested, this truck checks out for a wince-inducing $78,005 including $1,695 in destination fees. That’s a lot to pay for a tool, even if it is right in line with the competition. Skip a few highly desirable options — like the diesel engine and premium package — and you can get a base AT4 model for around 62 grand, which is a bit more reasonable.
Of course, if you need a heavy-duty truck, it really doesn’t matter what they cost. You can’t tow a horse trailer with a Toyota Corolla. The Sierra 2500 certainly has its strengths, even if rival trucks beat it in some important areas.