Brief: The 2019 GMC Sierra AT4

How does the 2019 GMC Sierra AT4 stack up? We’ll have to get briefly acquainted first before we can do a proper test.

First, I must preface this to say that this was part of a lunch even hosted by the Motor Press Guild in conjunction with GMC. This was done to allow MPG members a chance to look at the new 2019 GMC Sierra lineup. They also brought out an engineer, along with GMC’s communications people, so we could ask questions about it. It was held at the Proud Bird in El Segundo, CA which isn’t far from the Los Angeles International Airport (LAX). If you’re into World War II aviation history while getting a bite to eat, it’s certainly worth checking out while you’re in LA.

So, if you’re wondering why you’re seeing this at the same time as monthly and premium users, that’s why. However, if you want to get normal content up to two-weeks early and get exclusive galleries, videos, merchandise, and more, subscribe now.

The New Platform

The 2019 GMC Sierra and Chevrolet Silverado (and their SUV counterparts) are all built on the new GMT-T1 platform, better known as T1XX. It’s a complete redesign away from the K2XX of the 2013 to 2018 full-size body-on-frame truck/SUV platform. So, there won’t be much, if anything, that will interchange between the third and fourth generation chassis.

The T1 will have many engine options, probably one of the widest bredth of any full-size truck at the time of this writing. I say that because the LA Auto Show is coming up just after SEMA. There might be many new announcements made just after this publishes. We’ll be there to cover it but if you’re seeing this after either show, this bragging right might be outdated. Or not.

Anyhow, the T1 will take one of five engines – not including any variants – to power these full-size trucks. Ranging from the brand new 2.7-liter Turbocharged L3B four-cylinder to the LV1/LV3 4.3-liter V6 EcoTec3 to the 5.3-liter L83/L84 V8 EcoTec3 to the 6.2-liter L86/L87 6.2-liter V8 and the upcoming Duramax LM2 3.0-liter I6 Turbodiesel. Behind these engines will either be a GM 8LXX eight-speed transmission, 10LXX ten-speed transmission, and variants of the Allison they are so closely tied to in their Heavy Duty (HD) line.

The front suspension is a coil-over strut design and the rear is a leaf-spring setup. However, instead of having a forward rake, the truck sits level from the factory. Again, while it sounds like a factory leveled K2, there are design differences. The front spindle is taller versus the K2, which puts the upper control arm ball joint higher and outside of the wheel nearly equal with the tire sidewall. This changes the King Pin Inclination (KPI) and the steering axis, but the steering doesn’t feel heavy thanks to the electronic assisted power-steering rack. Much like my test of the Chevrolet Equinox, the steering doesn’t feel too light and dead nor too heavy. At least on the very brief 10-ish minute drive I had with it.

The brakes utilize an electronic hydro-boost unit, which is essentially a modern-day version of the old hydro-boost units found in HD versions of the K2 trucks. They just have an electric pump flowing hydraulic fluid rather than get their hydro-assist from the power steering pump. Kind of important considering there isn’t a power steering pump because the power steering is all electric now. It probably also frees up total manufacturing time as you no longer must fit a hydro-boost system to a diesel equipped chassis. If you’re unaware, diesels won’t have the vacuum required for proper vacuum assist power braking without using a vacuum pump or some other form of assist.


AT4 Features


What separates the AT4 from the other standard Sierras and Silverados is its suspension package. This lifts the truck up two-inches front and rear without spacers or blocks and using the X31 package – yes, this is a spring lift front and rear. This also adds a set of monotube Rancho shocks that are “off-road tuned.” So, think of this as the Trail Boss version of the Sierra. On the bumpy roads I drove around, it didn’t feel harsh, so I think I see what they are hinting at. It’s not the same as the Multimatic Dynamic Suspension Spool Valve (DSVV) shocks of the Colorado ZR2, that’s for sure. So, don’t expect hardcore, pre-runner-ish off-roading of the ZR2 but you’ll feel comfortable driving around areas around your campground.

Wheels and Tires

You get a selection of either 20×9.0 wheels with 275/60R20 All-Terrain Tires or a set of 18×8.5 wheels with LT275/65R18 Goodyear Wrangler DuraTrac tires, which this AT4 test truck did. Goodyear says this is a 32.3-inch outside diameter. The wheel design is exclusive to the AT4, a machined wheel face with dark grey paint in the cut outs and hub center. That machined face also features a dark clear coat, reducing the shine you’d normally get from something like this.


If you’re looking for some other off-road chops, you’ll be happy to hear that the 4WD system utilizes a two-speed transfer case and the rear differential has a locker in it. It also has a 3.23:1 Ratio for the 6.2-liter, but a 3.42:1 ratio is available with the Max Trailering Package. I’ll also lump in the Traction Select System and the Hill Descent Control here as that actuates some parts of the drivetrain, too. I didn’t try it in the AT4, but a Colorado I had tested had both and were superb units, especially the Hill Descent Control. When I tried it back-to-back against a Toyota Tacoma, the Tacoma sounded like it was about to fling something out of the hood while the Colorado was quiet. I didn’t even know it was activated until it got very steep.

You’ll also get the selection of the 10L80 transmission on top of the 8L90 that’s standard.


The standard engine will be the 5.3-liter EcoTec3 V8 and the Duramax 3.0-liter Turbodiesel when it comes out, but another option is the 6.2-liter EcoTec3 V8, which the test AT4 was equipped with.


Along with the Hill Decent and Traction Select mentioned earlier, you’re also going to get some trick tech in the AT4. The first thing you’ll notice – if the sun isn’t too strong – is the Multi-Color Heads-Up Display (HUD). I didn’t notice it much while I was driving the AT4 and – in some situations – when I was looking for it, I barely saw it. That’s the biggest drawback of any HUD that doesn’t have a polarized glass for it to shine on. So, that wasn’t much of a draw for me, but it wasn’t distracting either.

The piece of tech I was blown away with was the rear-view camera mirror. There have been rear-view camera monitors in mirrors before, but this isn’t that. The entire mirror is the monitor. It’s so well done I used it over the regular glass mirror. There is no latency, the view in the mirror is real-time and can be used as a normal mirror with extras.

With the camera located on the cab of the truck, you get a wide view by default. However, you can also zoom in to get a closer view of what’s going on behind you. If for some reason you don’t like that, you can flip it up to use it as a standard mirror as the monitor is behind a one-way glass. You also get the standard safety suite of surround vision, lane change alerts with the blind zone alert that rumbles the seat bottom, front pedestrian braking, and low-speed forward auto-braking.

The Aesthetics

You are certainly aware that the AT4 is an AT4. The front end has body-color grill surround, door handles and bumpers that already make it different from the Sierra and the Denali. What chrome that is there is done – save for the tailpipes and emblems – are in “dark chrome.” The fender trim is a matte dark grey color. What hits you when you see the front of the truck are the pair of bright-red tow hooks in the bumper. I’m rather surprised and maybe a bit disappointed that there wasn’t a badge for the 6.2-liter on the engine. It’s on the fenders, sure, but it should also be on the engine somewhere. It’s the biggest gas engine available for the Sierra. Come to think of it, The AT4 is a rather understated truck appearance wise – ok, save for the tow hooks – and I think one that modern full-size truck buyers will like more. There aren’t many younger buyers who are in to bright, flashy chrome on their vehicles even on their trucks.

Speaking of Looks

The Sierra is the better-looking version of the T1 truck platforms. Sorry, I couldn’t stay quiet about that. The Sierra’s front end is just more striking while retaining the aerodynamics applied into the Silverado while making it look so ugly. Even the trick that forces air to go around the front tires is retained. GMC was able to do that without looking like something is missing from the bumper. Chevrolet wanted a Camaro in truck form and used several ugly sticks to make it while the GMC is the superior design.

The Box

Rant over and we do so on an interesting part of the AT4, the pickup bed. Well, box as the marketing firms have now decided to call it. The biggest push on the entire Sierra line is how it was able to reduce 360-pounds without using all aluminum panels. They do use aluminum in the doors, hood and tailgate. They use steel in the fenders, roof, and the normal cargo box.

However, if you want to drop even more weight in the rear, you can opt for the CarbonPro – their carbon-fiber cargo box. They get from a supplier in Japan called Teijin via their Continental Structural Plastics division in Fort Wayne, IN. They’re not an unknown in this industry and are producers of carbon composites for the aeronautics, space and sporting goods industries. The other advantage is that the material is also thinner than the steel in the standard box. You gain about one-cu-ft more room in the CarbonPro box over the steel box that is already 5-ft, 9-inches or 63-cu-ft.

MultiPro Tailgate

You also get that awesome MultiPro Tailgate, the one thing every is raving about that only GMC has for now. When I first heard about it, I thought it was more gimmick than anything else. After using it in this test run, I’m surprised no one else has done it. In its fully folded out form, it’s a great bench seat and gives you an easy way to step into the bed while using the handle built in to the driver’s inner bedside.

If you want to prevent a load from sliding out from the bed while you have the tailgate down, that inner flap is handy while also working as a proper table when you have the tailgate up. To put it simply, it lives up to the hype that everyone is praising it for. Something that’s hard to say about most other things that sound like gimmicks on paper.

Initial Impressions

To be frank, a ten-minute drive around the El Segundo and LAX area isn’t much of a test drive. This is especially true for the AT4 since it’s specifically an off-road capable version of the Sierra. I’ve already spoken to GMC and, when a loaner becomes available for the West Coast region (it hasn’t even hit dealer lots yet), I’m going to get to drive one properly. I plan on taking it through the same paces as I did with the Honda Ridgeline Baja Chase Truck I did last year. In a way, they are very similar as to how they are done. Modest lift, selectable 4WD controls, and a ground-up redesign over their predecessors.

It wasn’t bad, the rough roads and construction around the Proud Bird were pleasant thanks to that suspension. I just don’t know how it does in the arena it’s meant for – the dirt. I don’t expect this to be a Raptor fighter and it’s not billed as such. I think it will do good on the dirt and be perfect for someone not looking for an all-out factory pre-runner like that, the 1500 Rebel and the Colorado ZR2. I certainly can’t wait to try it.



I feel like there is a great start to a fun truck in the 2019 GMC Sierra AT4. It has a great, off-road look from the factory thanks to the very aggressive looking Goodyear Wrangler DuraTracs at just over 32-inches in diameter, two-inches of suspension lift, and the lack of chrome. I would love to see it with a set of aftermarket off-road wheels, a set of 33- or 35-inch tall tires (seriously looks like 35s could fit with just that two-inch lift), and a set of shocks meant for harder off-road driving.

Also, it’s the better looking truck over the Silverado, you can’t argue that.


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Justin Banner

Justin Banner, Lead Editor and Founder of Carbage Online, has been involved with the automotive media and industry in many capacities and now tackles publication ownership with CarbageOnline.com. Prior to that, he has freelanced for top online publications of modern media that include Speedhunters, MotoIQ, Super Street Online, Hot Rod Magazine and many others. All due to his nearly 20 years experience as a mechanic, service writer, and technical support in the automotive industry. Justin is also a Journalist Level member of the Motor Press Guild - an industry recognized entity of professional automotive journalists - since 2015.