Back pressure in the downpipes, and not cold enough pfr plugs was causing a coking condition on my plugs which I think was causing my turbos to stop fully spooling about 5k rpm......I think. It kept me to 350whp and 380trq. Try those 3" expansives man, 7 or 8 degree ix's, and watch the hp line smooth out and start in the upwards direction. .