To ensure compatibility, ICON is no longer offering GM 2500HD/3500HD upper control arms as individual components. Upper control arms can only be purchased in unison with ICON shock absorbers as a complete system. The included ICON Vehicle Specific (V.S.) 2.5 Series shocks are designed and built to give your vehicle outstanding performance off-road and a smooth ride on the street. These shocks are configured specifically for each application in both length and damping tune. Like all of ICON's Shock Absorbers, the V.S. 2.5 Series shocks are 100% rebuildable and 100% revalveable. For piggyback and specific remote reservoir applications, ICON'S unique use of a 6061-billet aluminum manifold a few inches below the top cap of the shock creates an internal Bump Zone that when used creates an additional 20% of damping force. This additional force helps prevent harsh bottom outs and controls the suspension when compressing at high velocity. The ICON CDC Valve is an externally adjustable valve that restricts oil flow into the reservoir which creates 10 levels of compression damping force ranges.