The GMC Sierra AT4 1,000 Mile Off-Road and On-Road Review

My fingers prickled painfully as I wrapped them around the AT4’s heated steering wheel. They were finally beginning to thaw after packing up my frost-covered tent, but the transition from numbing cold back to warmth was giving my hands a less than delightful sensation. Fortunately, the drive was more than making up for that minor inconvenience. Simply put, it was magnificent. The Sierra Nevada loomed up in the distance, their snowcapped peaks piercing the pale morning sky in a stunning contrast of white and blue. Golden sunshine flitted through the dust swirling behind the truck, and mile after mile of desert landscape whipped by our windows while the Rancho suspension soaked up corrugations with buttery smoothness. The 6.2L V8 throatily rumbled along, playing a perfect bass to the guitar of my favorite songs on the stereo. I couldn’t help but smile at the perfection of the moment. Here, in the shadow of its namesake, the Sierra was home.

Two months ago we had the chance to spend a day with GMC’s Sierra AT4, a half-ton pickup truck aimed directly at vehicles like the TRD Pro Tundra, Ram Rebel, and Titan Pro-4X. With loads of ground clearance, a rear locker, upgraded suspension, and a host of off-road goodies it surprised us with its capability, but we were curious how it would handle a longer test off the groomed track. To find out, we decided to undertake a drive of extremes. We’d make our way from sunny San Diego to the sand dunes of Death Valley, wind our way up Route 395, and finally seek out a little snow in the mountains surrounding Mammoth. Along the way, we’d hike, climb, ski, and find out if the Sierra AT4 is really the do-it-all, off-road truck that GMC claims.

You can read our initial AT4 review here, where we dive into the specifications and off-road performance in more detail. For our long drive impressions, read on below.

The Gist

GMC’s Sierra AT4 is exceptionally comfortable to drive, achieved good fuel economy during our test, and was practical in daily life. It boasts impressive trail capability thanks to a host of factory off-road tech and will outperform most of its competitors on the dirt. The suspension is only average though, and the approach angle is ruined by the plastic air dam. We love that it’s equally at home on the trail or in the valet line for a downtown restaurant. Overall, the AT4 is a big win for GMC and a great option for anyone looking for a half-ton truck with real trail capability.

On Pavement and in Daily Life

Most of us build or purchase vehicles as if we spend 99 percent of our time driving down dirt roads and camping, but that’s simply not the case. The reality is that our lives will be consumed hammering out highway miles, running errands around the city, and generally keeping up with all the necessities of daily life. In other words, road performance matters, and there’s no doubt the GMC excels there.

Over the course of 1,000 miles spanning from San Diego to Mammoth and back, our AT4 averaged 20.1 mpg, with highway figures as high as 22 mpg. That was a shocker, as the EPA only rates it at 15 city and 19 on the highway, and the 6.2L V8 is an absolute fire breather, pumping out 420 horsepower and 460 pound-feet of torque when you put foot to floor. That will rocket the truck onto the highway, help you pass slow traffic, or tow up to 9,400 pounds to the sounds of an exhaust note so sweet it should be enjoyed in a symphony hall.

The rather good fuel economy didn’t give us much of an advantage when it came to overall range, as GMC only fit this Sierra with a 24-gallon fuel tank. While that theoretically gives the AT4 a reach of over 400 miles, a very competitive number, rough roads, low-range trail work, and a heavy payload will certainly cut into this.

As we noted in the initial review, piloting the Sierra AT4 down the road is a serene experience. The leather seats are wide and comfortable, the sound deadening is heavy, and there are features like heated seats and steering wheel, wireless charging, and Apple CarPlay to keep you comfortable and entertained. All of these aspects individually added to the enjoyment of driving the AT4, but what really stood out was the cumulative effect on our long drive. Usually, toward the end of a four- or five-hundred-mile day, driver fatigue will kick in. I’ll be tired, have a stiff back and sore neck, and be itching to get the heck out of the vehicle, but it just didn’t feel that way in this truck. The heated and supportive seats did a good job of relaxing my back, while the ability to simply watch the heads-up display eliminated the need for me to look down at the radio, navigation, or speed easing stress on the neck. It cruised down the road straight as an arrow, which meant I burned less energy staying in the lane and maintaining the speed limit. Even if we were to drift, the lane departure system would correct the situation and bring us back in line. The quiet cabin eliminates the need to speak loudly, so my voice wasn’t hoarse, and the engine’s ability to shut down cylinders kept the exhaust note down, at least until you get on the throttle. Basically, this thing eats miles, and you’ll love it for any road trips in your future.

We did find a few imperfections though. Specifically, the infotainment system would sometimes lag. This generally happened right after plugging a phone in, or after starting the truck when we tried to adjust the radio right away. On one particular occasion, the whole system crashed before rebooting and coming back online. Luckily, there were no issues after that.

One feature I hadn’t fully appreciated before this long drive was the WiFi. It’s not as useful on your daily commute unless you have kids that need to be entertained by streaming shows or movies, but on our trip, the ability to update the Garmin inReach, check emails, and upload content was a lifesaver. It not only eliminated the need to seek out coffee shops but enabled passengers to hammer out work on the drive so we could enjoy the destination when we reached it.

Of all the things I tested on this trip, I was prepared to be disappointed by GMC’s coveted Multi-Pro tailgate. Well, now I have to eat crow because we used multiple configurations of that darn tailgate every single day, and it is now one of my favorite features on any truck. The easy access mode made loading and unloading the bed an effortless process, as I didn’t have to strain my back to lift or shove the Yeti cooler in, or lean way over the tailgate to access items further back toward the cab. The step was useful for climbing into the bed but far better as a place to rest your feet while sitting on the tailgate or putting your boots on. We even used the load stop, a feature I deemed impractical in my last review of this truck. Yet there I was two weeks ago, wishing I had it on a surf trip when the board hung awkwardly over the back tailgate of the F-150 we were driving. Well, lesson learned. The Multi-Pro tailgate really is all it’s cracked up to be.

Long-term, Off-road Impressions

On our brief drive outside San Diego, we hadn’t really been able to open the AT4 up on corrugated dirt roads, so when we reached the first dirt roads north of Death Valley we didn’t hold back. With the Goodyear Duratracs at full air pressure, the Rancho shocks did a good job of soaking up the bumps and washboards with only minor vibrations and predictable handling. We did note that the tires picked up and subsequently tossed an inordinate amount of rocks though, occasionally flinging them into the fender liners with such force we jumped in our seats.

When the road became really rough, I aired down to 23 psi which made the AT4 feel more like a cloud than a pickup. There was very little chatter and the Sierra didn’t wander like many trucks tend to do on corrugations at higher speeds. When cornering on uneven or loose surfaces, the traction control system was largely imperceptible in its adjustments, only becoming heavy-handed when we laid into the throttle, forcing it to control the 6.2L V8’s thundering 420 horsepower. Of course, you can turn the traction control off, and you’re bound to have smiles as wide as your drifts.

The suspension felt good on dips, ruts, and rocks, but the AT4 is definitely under-dampened, which resulted in a sort of porpoising effect on larger impacts. In these situations, the system would compress, rebound to neutral, then continue to unload again before repeating the cycle two or three times. This got me curious as to what exactly GMC had used in their “2-inch suspension lift,” so I crawled underneath to find out. In addition to new Rancho shocks, it has upgraded front half shafts and jounce bumpers, but the lift actually originates from 2-inch spacer blocks. That’s not the end of the world, but it wasn’t really what we had expected from the suspension lift references in their media kits.

Thankfully, it doesn’t hinder the rest of the vehicle’s trail performance. In sand and mud, the AT4’s four-wheel-drive system did a great job of maintaining forward progress, while the rear locker kicked in any time the wheel spin differential became too great. Not that it usually did, as the 275/65R18 Goodyear Duratracs grappled their way over soft surfaces with ease while eagerly clearing out mud and rocks. Sometimes too easily clearing out rocks as we noted earlier. Nowhere was the system’s effectiveness more obvious than in the ice and snow surrounding Mammoth though. While other vehicles struggled to stay on the road, the Sierra cruised right by without the back end so much as stepping out. As the snow melted and the road became a patchwork of dry pavement and hidden ice, we switched to the automatic four-wheel-drive mode which made life a lot easier. The transition was seamless when the system kicked in, and I loved that it would only turn on when needed instead of forcing me to turn it off to perform tasks like making a tight turn into a parking spot.

In the tighter or more technical terrain surrounding Death Valley, I fell in love with the Surround Vision camera system all over again. It made seeing over the long nose of the truck less of an issue, and gave us the ability to self spot our way through difficult parts of the trail. My favorite aspect was the overhead 360-degree view, which made turning around on trails, or even parking in Los Angeles a much easier task. One thing I wished it featured was a mode that showed the terrain ahead of you with the side camera views of the wheels as well. Without this, you’re always flying blind in one area or another. You can either see the rock closing in on your doors, or the rocks in front of you, but not both.

The ground clearance was ample for everything we threw at the AT4, but you’d expect that since its 10.88 inches of clearance is more than the Ram Rebel, TRD Pro Tundra, Ford F-150 or Nissan Titan Pro-4X. Unfortunately, the front air dam was still an issue, as it ruins the approach angle, reducing it to a measly 25.8 degrees. The departure angle was never an issue, but with the running boards equipped was awfully close to finding the limits of breakover on a few occasions. We probably would have, but GMC requested we not do any difficult trails without their supervision, so we have to defer to our previous impressions of this truck’s performance on the rocks, which you can read about here.

Conclusions

After 1,000 miles with the AT4, I can say a few things for sure. First, it’s quite practical for daily life thanks to decent fuel economy, great cameras, the world’s most useful tailgate, and aggressive off-road looks that still fit in at black-tie events. Second, the suspension will get the job done, but if you’re looking for better than stock performance or additional lift we would switch to an aftermarket kit like the one offered by Icon Vehicle Dynamics. Third, when it comes to road trips, the AT4’s big motor, comfortable interior, and abundant electronic features make it a prime choice.

Fourth, and finally, we learned that GMC got this truck right, and it is far more than a tough appearance package on a luxury pickup. It will climb hills, conquer snow banks, and have you grinning ear to ear as you race down desert tracks in the comfort of a quiet cabin. If you want a vehicle that can hit the trails, tow a trailer, and still take your friends out for dinner downtown, the Sierra AT4 will fit the bill.

To learn more, visit the GMC website here. 

Born and raised in Dallas, Texas, Chris didn’t receive a real taste of the outdoors until moving to Prescott, Arizona, in 2009. While working on his business degree, he learned to fly and spent his weekends exploring the Arizona desert and high country. It was there that he fell in love with backcountry travel and four-wheel drive vehicles, eventually leading him to Overland Journal and Expedition Portal. After several years of honing his skills in writing, photography, and off-road driving, Chris now works for the company full time as Expedition Portal's Managing Editor.