1999-2019 Duramax Rear 7-10" Lift FOX Performance Series 2.0 IFP Shock (980-24-958)Fox Racing Shox 2. 0 Performance Series IFP smooth body shocks deliver race dominating performance in a hassle free bolt on package. Their heat reducing design includes a metal impacted aluminum shock body that dissipates heat faster than conventional steel. Inside, the Internal Floating Piston (IFP) separates the shock oil from a high pressure nitrogen gas chamber, providing a predicable ride quality capable of handling the roughest road conditions.