Taking GMC’s New AT4s Off-Road Looking for More

At the launch of the 2020 Sierra HD and 1500 Duramax, we got the chance to take the slow road in the new AT4 versions of both trucks.

GMC had set up three different courses because the different types of off-road driving are extremely varied. The first loop was the most fun, but probably not what you’re going to spend most of your time doing off pavement.

It started off with a drive up a 15 degree or so slope of large loose rocks. A little too loose, it turns out. Somebody had tried to make the hill more challenging, and things got far more exciting because of it. The two-inch lift of the 1500 AT4 was no match for watermelon-sized rocks that were moving around the face of the hill. Look closely at a few of the photos and you can see the fist-sized dents they’d left in the rocker panels. And I’m surprised that there was still a lower bumper trim left on this truck.

That might actually be one of the most challenging parts of off-roading. Putting the first rock dent on your $70,000 truck. Maybe it’s like the first parking lot ding. Frustrating but liberating. It’s not perfect anymore. At least unlike the parking lot ding, you did this one yourself. More importantly, the underbody skidplates are doing their jobs, since some absolutely bone-shattering impacts directly under the engine haven’t painted the rocks with gear or motor oil.

By my turn, the GMC course workers had wisened to the nearly impassable rock face and moved some of the rocks. Which is what you’d do yourself if you saw a stack of small boulders in your way. And you would see them, thanks to the front-facing cameras that make it a whole lot easier to pick your way around a trail.

We’re firmly in 4WD Lo-range. Loads of torque from the 3.0L inline-six diesel and all that gearing makes getting up the hill easy. It won’t quite idle up, but low range means that big presses of the pedal don’t send you rocketing over the other side. The locking rear diff is engaging seamlessly to keep this rig moving. And the engine’s so quiet I didn’t realize it was the oil-burner until GMC pointed it out.

It’s cresting the hill where the front-view camera is most impressive. Because without it, there’s no way I could see the other side short of leaning out the front window dangerously. The inclinometer on the HUD is neat too, but I’m not coming anywhere near the tipping point, so it’s not all that needed.

Up next is the mud hole. Since I already know it’s not sink-the-Bismark deep, it’s aim for the center and flatten the throttle. This is the most fun part of going off-road. Splashing in mud puddles until you can’t see out the windows anymore. Then turning around and doing it again. If you don’t find joy here, then check your pulse because it might have stopped. Or it’s just not your jam. Hey, you do you, but you should give this a try at least once.

These trucks don’t have 10 off-road modes on the dash. There’s not even one, in fact. Even the Acadia gets an off-road mode! But you don’t really need them. Especially with 4Lo. And there is a hill descent control button if you need to let the computer handle getting you down a particularly steep incline without worrying about tire lockup.

As much fun as it is making a big mess, that’s not really the point of the AT4. If you want to go jumping and rock crawling all the time, the Colorado ZR2 might be more the ticket. GMC says that the AT4, especially the HD version, is more about twin-track running when you need to do some work, too.

And really, that’s what they’re better at. Picture heading down a dirt road to the cottage with a load of gear in the bed. Or traversing a field with farm equipment loaded. Or hauling firewood back to the cabin. Or even towing a boat to that far-away fishing hole. That’s what the AT4 is best at.

That doesn’t mean it isn’t fun. GMC had us playing with the LD AT4 on a fast and wide-open stretch of dirt track, and the Rancho shocks do an exceptional job of both controlling the body and making it more comfortable. All-terrain tires aren’t just for muddy grip, they’re for making sure you don’t cut soft sidewalls or tread blocks when you hit that gravel or rock going a little bit too fast. A healthy shot of diesel torque in 2WD mode and the back end of this pickup is happy to play. It puts a smile on my face faster than any hot laps, and you can do this with five people on board.

After getting sideways in the 1500, it was time to take the HD off-road. This was a deeply rutted two-track. A farm field perimeter road. Probably worn in by generations of tractors plodding along between work and barn. A stock-height truck could easily find sump and hump – that’s the oil sump and the hump between the ruts – making horrible oily contact. The lift and shocks reduce that possibility. And to show us that the AT4 HD is ready for work, we’ve got more than 2,000 lbs of logs in the bed. Fortunately, they’re really well strapped down because I’ll admit I forgot about them for a few minutes of high-speed fun. The first-in-HD automatic transfer case means I can leave it in auto and get 2WD when I’m just pounding along the grass, but engage 4Hi as soon as the wheels start to spin. Not exactly donut friendly, but it’s designed to keep you from getting stuck when surfaces suddenly change.

Running through tall grass, smelling the fresh air, and kicking up a trail of dust behind you. It’s loads of fun. And you can do it in just about any pickup or SUV if you watch your speed. But trucks like these AT4 Sierras are modified to be more happy about it. With shocks that make it more comfortable and underbody protection to help keep the vehicle healthy. The AT4s will also let you do it with a bed full of gear. Which GMC figures will be perfect for a whole lot of buyers.