Fox 2.5 HTO Performance Rear Shock | Single | 0-1 in Lift | 2001-2026 GM 2500HD/3500HD

Fox 2.5 HTO Performance Series Rear Shock | Single Unit | 0–1" Rear Lift | 2001–2026 Chevy Silverado / GMC Sierra 2500HD & 3500HD

The Fox 2.5 HTO Performance Series rear shock (SKU: AX4009) is a step-up heavy-duty rear shock engineered for 2001–2026 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD trucks running stock height or up to 1" of rear lift. The larger 2.5" aluminum body increases oil volume for superior heat capacity and fade resistance vs. the Fox 2.0 (AX664). HTO (High Travel Output) valving delivers controlled, consistent damping under sustained towing, hauling, and rough-road conditions. The IFP (Internal Floating Piston) design separates oil and nitrogen gas to maintain consistent damping through heat cycles. Tuned specifically for the GM HD chassis — not a universal shock. Sold as a single rear shock.

Verified Fitment (OFAS Standard)

• Chevy Silverado 2500HD (Rear): 2001–2026 — stock height to 1" rear lift
• Chevy Silverado 3500HD SRW (Rear): 2001–2026 — stock height to 1" rear lift
• GMC Sierra 2500HD (Rear): 2001–2026 — stock height to 1" rear lift
• GMC Sierra 3500HD SRW (Rear): 2001–2026 — stock height to 1" rear lift

Does NOT fit: Silverado/Sierra 1500 (different rear suspension geometry). Does not fit trucks with more than 1" of rear lift — a longer-travel shock is required. Not compatible with long-travel or coilover conversion systems. Verify fitment on 3500HD DRW (dually) configurations — rear suspension geometry may differ from SRW.

Fox 2.5 HTO vs. Fox 2.0 (AX664)

• Body diameter: 2.5" (vs. 2.0" on AX664) — greater oil volume, superior heat capacity
• Valving: HTO (High Travel Output) — tuned for sustained heavy-load damping vs. standard IFP valving on AX664
• Price: $346.95 (vs. $229.95 for AX664) — recommended for high-frequency towing, max payload, or extreme duty cycles
• Weight: 8 lbs (vs. 7 lbs for AX664)

Technical Specifications

• SKU: AX4009
• Series: Fox 2.5 HTO Performance Series
• Position: Rear
• Quantity: Single shock (order 2 for a complete rear pair)
• Body: 2.5" aluminum — increased oil volume vs. 2.0" Fox 2.0
• Damping: HTO valving + IFP (Internal Floating Piston)
• Lift Range: 0–1" rear lift
• Weight: 8 lbs
• Application: High-frequency towing, max payload, sustained heavy-duty use

Installation Notes

• Sold as single: This listing is for one (1) rear shock. Order quantity 2 for a complete rear replacement pair.
• Lift confirmation required: Verify rear lift height is 0–1" before ordering. Installing on a truck with more than 1" of rear lift will result in incorrect shock travel and potential bottoming or topping out.
• Torque specs: Upper and lower mounting hardware — torque to OEM specification for GM 2500HD/3500HD rear shock mounts (verify in Fox install sheet or GM service manual).
• DRW verification: If running a 3500HD DRW (dually) configuration, confirm rear shock mounting geometry matches SRW spec before ordering.
• Replacement interval: Inspect for oil weeping, fade, or excessive body heat after installation. Fox 2.5 shocks are rebuildable — retain the shock body for future service.
• Pairing note: For optimal handling balance, replace rear shocks in pairs. Mismatched damping rates between left and right will cause instability under load.

Installation Warning

Do not install on trucks with more than 1" of rear lift — incorrect shock travel will result in bottoming or topping out under load. This shock is not compatible with long-travel or coilover conversion systems. Sold as a single unit — verify quantity before ordering. Once installed, the unit is non-returnable.

What is your current rear lift height, tow/payload frequency, SRW or DRW configuration, and are you replacing one shock or a complete rear pair — confirm whether the 2.5 HTO or Fox 2.0 (AX664) is the right spec for your duty cycle?