The Chevrolet Z71, X31 for the GMC trucks, packaged some off road oriented upgrades over the LT and SLE model trucks. In the 2019-2021 Silverado 1500 Z71 and the 2019-2021 GMC Sierra 1500 X31 packages, customers were given a dual speed transfer case, steel skid plates, Hill Descent Control, All Terrain tires and Rancho Twin Tube shocks.

GM took these upgrades further with the introduction of the Trail Boss and AT4 Packages. Chevrolet did offer a Trail Boss package in 2016 but that was short lived and only offered for 1 year before being discontinued. With the new Trail Boss and AT4 packages, GM gave customers a 2” lift in the front and a 1” lift in the rear supported by Rancho monotube struts and shocks tuned specifically to GM’s specifications, higher angle CV axles to accommodate the extra lift and factory 275/65 R18 tires.

Factory Suspension Basics

• 2” factory lift over the Non Trail Boss and AT4 models
• GM specced Rancho Monotube
• 2” lift strut 1” Rear Block
• Come with 275/65 R18

Existing lift system being replaced by aftermarket options, stacking lifts, upper arms.

Aftermarket Suspension Options

Bilstein

One of the biggest complaints about the factory Rancho suspension on the TrailBoss and AT4 trucks is that they are too soft and “boaty” feeling. If you are looking to simply improve that ride quality on road, the Bilstein 5100’s will solve those issues for you while still also allowing you to level the truck with up to an additional 1.1” of lift on the front of the truck.

However, if you are looking to step up the ride quality both on and off road with a capable suspension setup to handle the larger bumps and washboard roads, the Bilstein 6112’s and their 2.6” diameter shock paired with the 5160 reservoir shocks in the rear will handle those tasks and are the perfect setup some people looking into getting into more serious off roading.

FOX

Fox offers both their Performance 2.0 and Performance Elite Series 2.5 options for the Trail Boss and AT4’s. For customers looking to keep factory height, but improve off road ride quality while keeping the budget low, the Performance 2.0 is the ticket for you. The aluminum shock bodies are going to help with the heat dissipation without the need for an external reservoir.

Fox took this a step further with the new addition of their Performance Elite 2.5 series. With the Performance Elite line of Fox shocks you are getting a CNC machined 2.5” diameter body along with reservoirs and Fox’s Dual Speed Compression (DSC) adjusters. With the DSC adjusters, you are able to adjust the high speed compression and the low speed compression independently to really dial in the ride quality for the specific terrain that you are going through on any given trip. Your low speed compression will be your slower shocks shaft movements (body roll, brake diving, g-outs at the transition of a sand dune) while the high speed compression adjustments allow you to tune for the faster shock shaft movements (washboard roads, potholes).

Icon Vehicle Dynamics

Icon Vehicle Dynamics was the first suspension company to introduce their Stage series of suspension systems. This made it easier on the customer to pick something in their budget. With this being said though, everything in their stage series is available for purchase separately. If you are looking to add some additional height to your Trail Boss or AT4, you will want to look at the Stage 2 or higher suspension systems. These systems will offer up to 1.5” of additional lift height over the factory setup. These stages will also include the option of having a steel tubular UCA or a nice looking billet aluminum UCA, with both featuring Icon's popular Delta Joint.

Icons Stage 2 kit features a 2.5 series extended travel non reservoir coilover for the front and 2.0 series rear shocks. Stepping up to the Stage 3 system, you will get the same coilovers in the front, but with the added reservoir and the rear shocks get upgraded to 2.5 series shocks with piggyback reservoirs. Now if adjustability is what you are after, look at the Stage 4 system. With the Stage 4 system you get Icons tried and true CDCV valve. This is going to be your mid range compression adjuster offering 10 levels of adjustment to get you dialed in for any street or dirt driving you plan on doing.

King

Everybody knows that color once you see it. Once you see that blue in someone's wheel wells, you already know King is what they are riding on. King shocks have been on the podium for any off road race you can think of and what many off road racers trust to get them to the finish line.

King has both 2.5” and 3” coilover and shock options for the Trail Boss and AT4. The 2.5 series are a great upgrade and will handle everything most of us can dish out to them, but if you are the type that likes to get rowdy out in the dirt and drive faster than our abilities can handle, the 3.0’s are going to be what you want to look at. The massive 3” piston allows for more damping force to help soak up all the rough stuff. To match up the front 3” coilovers, King has come out with a 3” internal bypass smooth body shock with the compression adjusters that you would find on the front.

Frequently Asked Questions

Whats the big differences between the Trail Boss and AT4 models compared to base Silverados and Sierras? Can the suspensions be shared?

The biggest difference between the Trail Boss/AT4 and the base models is going to be the suspension. The Trail Boss/AT4 came from the factory with a 2” lift in the front and 1” in the rear. Bilstein is the only manufacturer that has specific part numbers for the Trail Boss/AT4. Fox, King and Icon share the same part numbers for the Trail Boss/AT4 and the base models.

How much can I lift the front of the truck before I need UCAs? Do I need new UCAs when I do a leveling kit on my Silverado/Sierra?

In terms of alignment, we find that anything over 2.5” of lift will require an aftermarket upper control arm. With that said, any coilover capable of 2.5” of lift or more should be paired with an aftermarket upper arm regardless of the lift height they are set to, to avoid ball joint bind or contact with the coil and stock arm.

When do I need a differential drop?

Generally, we recommend a differential drop on spacer style lifts over 2.5” or with any coilover capable of achieving over 3” of total lift.

How do I know what UCAs to run? (Small Taper vs Large Taper Ball Joint) How do I figure out what upper control arms my Silverado/Sierra have and which ones to buy?

From 2007 to 2018 GM used three different kinds of upper control arms with two separate ball joint sizes. Vehicles with Aluminum (silver) or stamped steel (black sheet metal) upper control arms use aftermarket upper control arms with large taper ball joints. Vehicles with black forged steel upper control arms use aftermarket upper control arms with small taper ball joints.

What size tires can I run with most 2-3” leveling kits?

In most cases, you can run up to a 33x11.5 or equivalent size in tandem with an aftermarket wheel with a 0 offset or lower with minimal to no trimming. Backspace will vary on rim width.

Do I need the shocks with the reservoirs?

This is dependent on how you are using the vehicle. If during any of the driving you are doing you see a marked degradation in ride quality over the duration of the trip, trail run, or off-road trek it may be a good idea to upgrade to a shock with an external reservoir.

What kind of shock do I need to reduce all the body roll and bounciness from towing?

We typically recommend a monotube shock to properly dampen heavier loads, whether thats in the bed or hitched up like a toy hauler or trailer. Shocks like Bilstein 4600s, 5100s, Rancho RS7MTs, KYB Monomax, are all significantly better than stock shocks in handling loads.

What is a good budget beginner off-road shock?

On a budget, the Bilstein 6112’s (Front) and 5160’s (Rear) are very hard to beat. On the front, you get a 2.6” shock similar in size to the Fox, King and Icon 2.5 series coilovers and the rear you get a 46mm (2”) piston shock with reservoirs. All for a similar cost of a set of coilovers from the other brands.

What are the best off-road shocks available for the Silverado & Sierra?

This depends on the kind of off-road driving you will be doing. If you want the best off-road performance and like being out in the desert, the linear valve of the Fox and King suspension is what you would want to go with. King has 3” series suspension for the Silverado which use a 3” piston in the front and rear, with the rear being external bypass shocks. This will give you the best performance off-road without going with a long travel setup. If you are getting together an overlanding type of build, where you need the suspension to perform as good on-road as it does off-road with the heavier builds, the digressive valving in the Icons is the way to go. Fox, King and Icon all have adjustable damping options that are also worth taking a look in to.

What kind of shocks do I need for my 4” / 5” / 6” lift kit?

For most lift kits on the market, for the 2007+ GM 1500 platform, the lift systems typically use strut spacers on top of the factory front struts to achieve the 4”, 5”, or 6” of total lift. For the rear, typically a lift block or add-a-leaf pack is used to achieve 4” or 5” of lift; a height that keeps the vehicle level front to rear so this sometimes varies.

So for these lift systems, most people replace the front struts with factory height struts, and then replace the rear shocks with extended length shocks.

Most shock manufacturers do not produce extended-length struts, and if they do, they’re just creating an extended mount on a factory-like strut. So even though there is a 6” lift kit, that doesn’t actually mean there’s 6” more of travel from the front suspension/struts; the lift was achieved by relocating various suspension components down, relative to the chassis of the vehicle.

If I buy new struts, do I need new springs?

Aftermarket struts will use the factory springs.

Most coil springs can easily last 200,000 miles on a daily driven vehicle. If the Silverado has been used heavily as a work vehicle, then the life of the springs will degrade more rapidly, and its advised to change them out once the vehicle hits 200,000 miles, or sooner, depending on overall suspension health.