Expert Reviews

2021 GMC Sierra AT4 Diesel Review

AutoTrader SCORE
This score is awarded by our team of expert reviewers after extensive testing of the car
  • Safety

The immense popularity of pickup trucks and the need for companies to make these big beasts as fuel-efficient as possible has led to a myriad of engine choices in the Detroit Three’s offerings.

In my 2021 GMC Sierra AT4 tester, I got a 3.0L turbodiesel. It’s the mid-priced engine of the three available in this off-road-ready trim level, between 5.3L and 6.2L V8 engines (both of which are gas-fired). The AT4 starts at $63,498 and mine had numerous options added to it, including a carbon-fibre composite bed, bringing it to $76,168 before freight and taxes.

Styling: 8/10

While the Sierra shares its body and mechanicals with the Chevrolet Silverado, I’ve always thought the GMC was the better-looking of the two. I prefer the GMC’s squared-off grille to Chevrolet’s split-front affair.

The AT4 comes with a two-inch lift kit and 18-inch wheels, which almost look tiny in an era where higher-end trucks sport 20-inch hoops, but you want a decent amount of sidewall for off-road driving. Inside, I think the cabin styling lags a bit behind the Ram 1500 and Ford’s redesigned 2021 F-150, but it still looks okay on its own merits, and it’s put together well.

Safety: 8/10

The United States National Highway Traffic Safety Administration (NHTSA) gives the Sierra four stars out of five overall in crash testing; it earned the full five for side-impact, but four for frontal crash and rollover (four for rollover being the norm for just about every vehicle out there). The Insurance Institute for Highway Safety (IIHS) gave it the highest “good” rating for driver’s side small overlap, moderate front overlap, side, roof strength, and head restraints and seats; but only “marginal” for passenger-side small overlap. It also got “marginal” for child-seat latch ease of use.

My tester had several high-tech safety assist features, although they were spread across a few packages. These included emergency front braking with pedestrian detection, lane-keeping assist, automatic high-beam headlights, blind-spot monitoring, cross-traffic alert, and front and rear park assist, plus the rearview camera that’s mandatory on all new vehicles. I also had a “Safety Alert” seat, which vibrates as a wake-up call for lane-departure, collision, cross-traffic, and other warnings. It’s very effective but also very startling if you’re not used to having your seat go off.

Practicality: 9/10

The Sierra has the inherent practicality of a pickup, of course, and in my tester’s configuration has a maximum towing capacity of 4,445 kg (9,800 lb), and payload of 700 kg (1,544 lb). Inside, there’s a ton of small-item storage: a large open centre cubby, deep console box, two gloveboxes, and a bin atop the dash. The rear seat cushions lift up to reveal a storage area under them, and the seatbacks cleverly conceal storage bins inside.

The CarbonPro bed is part of a $4,790 option package. The box exterior is steel, but the floor and sides are made of carbon-fibre composite. The idea is that it saves weight – about 27 kg (60 lb) – and also resists dents and corrosion. Three indentations at the back are meant to hold the wheels of bicycles or dirt bikes. My truck also had a MultiPro tailgate, which features a small gate-within-the-gate. This can be configured six ways, including as a bed step (with a handle in the bed side), cargo stop, or two-tier loading. An ultra-simple-and-brilliant bumper step, with a hand-hold in the box side, is standard equipment.

User Friendliness: 9/10

I like simplicity in my vehicle controls, and the Sierra delivers. Temperature and fan speed are controlled by dials, and the heated-and-ventilated seats work with toggles. There are dials for the stereo volume and tuning, and the touchscreen’s icons are large and intuitive.

The steering-wheel controls are equally simple, with buttons or thumb-wheels for the cruise control and other functions. There are also buttons for the four-wheel drive system, and a dial for the drive modes. However, I noticed one glitch: the navigation and head-up display both show the speed limit of the road you’re on, which I’m assuming it does through GPS (some systems actually read the road signs). On many roads, both city and major regional rural roads, the display stayed blank or posted an inaccurate speed. I wasn’t depending on it, but still, the system should have done a better job.

Features: 8/10

On its own, the AT4 comes very well equipped – as it should for its $64,000 starting price, of course – including LED front and rear lighting, auto-dimming and power-folding mirrors, power tailgate (up and down), and twelve fixed cargo tie-downs. On the inside, you get heated and ventilated front seats with 10-way power adjustment, heated rear seats, dual-zone automatic climate control, a heated steering wheel, and auto-dimming rearview mirror.

But you can certainly pack more into it and mine did, which added such items as a camera mirror (which plays a digital version of what’s behind you on your rearview – handy if the bed’s contents block your mirror, although I find it tough to quickly focus on it), head-up display, power sunroof, power-sliding rear window, and assist steps.

Power: 8/10

The Sierra lineup offers five engine sizes, including a turbocharged 2.7L four-cylinder and 4.3L V6, but the AT4 has a choice of three. The base engine is a 5.3L V8 making 355 hp and 383 lb-ft of torque. I had the optional 3.0L inline-six turbo diesel, which makes 277 hp and 460 lb-ft of torque, which added $3,245 to the bill. The third choice is a 6.2L V8 that makes 420 hp, and the same 460 lb-ft of torque as the diesel. The transmission is a ten-speed automatic.

All three of the Detroit automakers now offer small diesels in their half-tons, and GM’s version sits mid-pack for torque. Ford’s 3.0L V6 engine makes 250 hp and 440 lb-ft of torque, while Ram’s, also a 3.0L V6, produces 260 hp and 480 lb-ft.

Comfort: 8/10

Most people will want my tester’s optional side steps. Like all full-size pickups today, the Sierra is needlessly oversized and it’s a long step up, although there are grab-handles at all four doors to help you in.

The Sierra’s seats are well-sculpted and have enough bolstering for good support. They’re both heated and ventilated, and the rear chairs are heated as well. I had no trouble finding the right driving position and visibility is good, especially since there’s some space between the outside mirrors and the body – on some trucks, no doubt in the interest of aerodynamics, the mirrors are tucked in closely, so the windshield pillar and mirror can combine to create a blind spot that can hide a pedestrian.

Driving Feel: 8/10

The Sierra is a big truck but it responds well to steering wheel input. I’d put its handling a notch below the new Ford F-150, which drives smaller than it is, but above the Ram 1500 and Toyota Tundra.

The diesel is a great engine: smooth and strong, with linear acceleration and power whenever you need it, whether off the line or for passing on the highway. The ride is comfortable and composed. That was a high point given the AT4’s off-road chops, since many tough-stuff-capable trucks can have an annoyingly undulating ride on hard pavement. Speaking of that, in addition to high- and low-range gearing for the four-wheel drive system, which should only be used on loose surfaces to avoid driveline damage, the AT4 includes an automatic setting for use on asphalt. That’s handy if a road has alternating patches of snow and bare pavement.

Fuel Economy: 8/10

My tester’s 3.0L diesel is officially rated by Natural Resources Canada (NRCan) at 10.5 L/100 km in the city, 9.1 on the highway, and 9.9 L/00 km in combined driving. I had the truck in cold weather and averaged a much higher 13.3 L/100 km, without any towing or payload.

Comparing official numbers, the Detroit light-duty diesels are all pretty much in the ballpark. Ford’s V6 averages 10.7 L/100 km in combined driving, while Ram’s V6 comes in at 9.7 L/100 km. All three require diesel exhaust fluid (DEF), which is automatically squirted into the exhaust system to help minimize tailpipe pollution. Automakers generally size the DEF tank so it gets refilled during scheduled maintenance, but if it’s necessary otherwise, you can buy the fluid at parts stores or most gas stations, and it goes in beside the fuel filler.

Value: 7.5/10

It’s always hard for me to put “value” and $76,000 in the same sentence, but for those willing to spend, you do get a lot of features with the AT4 trim level, and you don’t need to add all the options that were on my truck.

The big thing for many buyers is stepping up to the diesel. These engines are popular – I love driving them – but there can be more than meets the eye, starting with the $3,245 this one adds to the price. Oil changes cost more than with a gas engine, you have to add DEF, and while they are more fuel-efficient, you’ll only get that back if you put on enough kilometres. They do tend to give a truck a higher resale value, but do your math before you open your wallet.

The Verdict

Everybody makes good trucks these days. While you may have sworn loyalty to a specific brand, it’s always in your best interest to look around and see what the “other guys” have to offer, which may better suit your needs and budget. The Sierra has lots of good points, and might very well be the one for you.

Engine Displacement 3.0L
Engine Cylinders I6
Peak Horsepower 277 hp @ 3,750 rpm
Peak Torque 460 lb-ft @ 1,500 rpm
Fuel Economy 10.5 / 9.1 / 9.9 L/100 km city/hwy/comb
Cargo Space 700 kg (1,544 lb) payload
Model Tested 2021 GMC Sierra AT4 Crew Cab
Base Price $63,498
A/C Tax $100
Destination Fee $1,900
Price as Tested $78,168
Optional Equipment
$12,670 – AT4 CarbonPro Edition (carbon-fibre composite bed, garage door opener, power-sliding rear window, premium infotainment system with navigation, Bose premium sound system, wireless charging, 18-inch Goodyear Wrangler DuraTrac tires, front and rear park assist, blind spot monitoring, rear cross-traffic alert, high-clearance step), $4,240 after discount; Technology Package (HD Surround Vision, rear camera mirror, bed-view camera, head-up display, 8-inch driver information centre), $2,520; Driver Alert Package II (forward collision alert, lane-keep assist, automatic emergency braking, front pedestrian braking, automatic high-beam headlamps, adaptive cruise control, following distance indicator, Safety Seat alert), $1,260; Power sunroof, $1,325; 3.0L Duramax turbodiesel, $3,245; Wheel locks, $80