Duplicate post; covered in your "Flywheel lock" thread. But the link above is very informative, too.
2004.5 Silverado 3500 SRW 4x4, D/A (LLY), Ext. Cab, Long Bed
engineer837 aux rad, TxC CAI, LBZ MP, Scangauge II, Nicktane aux filter head, KD lift pump, 2008 PS pump, 2011 hydroboost, Frederico Swaybars, Rancho 9000XL, Torklift StableLoads, BFG AT/KO2, Lance 835 Camper often in the bed.