1996 gt fuel pressure problem. Already replaced several parts.

I have a 1996 Gt 5-speed. It has ran great since i bought it. Up to a couple of weeks ago it started bogging down while running. Idles really hard sounds like i have huge cams then dies. It turns over and over with no luck.(just ocational start ups with it camming real hard then it dies again) I wait about 30 min, then it cranks up fine does that every other day or so. Already replaced IAC, cam sensor, fuel filter, fuel pump,fuel pressure reg. Fuel pump sorta fixed it for bout two weeks. bogged down, cammed, then cut off again. Injecters don't leak with ignition on engine off, just tested that. Maybe faulty puel pump? Cuz even with the new pump fuel pressure was low and it would bogg down while acceleration (lost to an 89 cuz of it) Fuel pressure is about 15 psi. and quickly released pressure leaking somewhere. Please help done ran it through all the shops around here dont care how much it costs to fix it just need it running again.:worship