My belt slips horribly after ~3800-4000 rpm(depending on temp). I go from about 12-3 psi to 8-9 psi. Mind i do have a full exhaust/CAI as well. Im not sure if i have a 5 or 10% pulley on, but it is a gatorback 4080392 on my blower. the belt has alot of evidence of slippage on it. I need my boost back so i can beat these Stangs again!