i own a 1988 thunderbird turbo coupe. the car seems to loose power around 3,500 rpms or so. it seems like it flattens out. i have an adjustable boost valve on it and it runs a t 18 psi where i have it set at. ive installed new plugs, wires, cap, rotor, checked for vacuum leaks, checked fuel pressure, i'm not getting any engine codes, it's a 5 speed. anyone one have any ideas???