The 2500HD AT4X and ZR2 models were first introduced by General Motors in 2024, with GM advertising a 1.5-inch factory suspension lift. However, direct comparison to standard 2500HD models tells a more detailed story.

Our measurements show the rear lift claim is accurate at 1.5 inches, but the front ride height increase is actually closer to 2.5–3 inches over standard models. Rather than a true front lift, the AT4X/ZR2 configuration is better described as:

• A front leveling-style height increase

• Combined with a 1.5-inch rear lift block

This distinction matters because the front height increase is not achieved with a subframe drop or taller steering knuckle, which are typical components of a true suspension lift.

The increased front height comes from a combination of component changes:

• Lower control arm with different torsion bar clocking, increasing lower arm angle at ride height

• Repositioned bump stops

• Lower control arm length increased by 0.2 inches to restore track width

• Upper control arm length increased by 0.2 inches

• Modified knuckle neck shape, while maintaining the same critical suspension geometry as standard models

While effective at increasing ride height, this approach does not increase suspension droop travel—and that’s where issues arise.

Although the AT4X/ZR2 gains additional up travel, it suffers from only 2-1/8 inches of front droop travel in stock form. That’s 1 inch (approximately 35%) less droop than standard 2500HD models.

The result:

• Noticeable front shock top-out

• Harshness over dips and on the backside of speed bumps

• Reduced suspension compliance off-road

Additionally, the increased ride height places additional stress on the pitman and idler arms, accelerating wear—an issue long associated with GM HD steering systems.

Cognito offers a patented solution to this problem with their Pitman & Idler Arm Support Kit (PISK). While not included in the standard factory configuration, it is highly recommended to restore steering durability and precision.

This standard lift kit package addresses the factory shortcomings by converting the AT4X/ZR2 front suspension into a true engineered lift system.

Front Suspension Improvements

• Adds a subframe, taller steering knuckle, and differential drops

• Provides 2.5 inches of additional front ride height

• Increases front droop travel to 3 inches, meeting Cognito’s minimum standard

• Differential drop maintains proper CV axle angles

• Includes a Non-Torsion Drop Bracket to keep torsion bars properly positioned in the frame

Rear Suspension Adjustments

• Replaces the factory 1.5-inch rear block with a 2-inch block

• Net rear lift increase of 0.5 inches

• Includes longer U-bolts for proper clamping and safety

This package retains the OEM Multimatic DSSV shocks:

• Front shocks use a billet extended lower clevis mount to accommodate increased height

• Rear shocks remain unchanged due to the minimal rear lift increase

For owners seeking maximum suspension travel, improved damping control, or enhanced off-road performance, upgraded packages with aftermarket shocks and control arms are strongly recommended.