I have a '95 GT and have been experiencing a really bad running car at partial throttle. It misses and somtimes pops. DTC shows # 543 which = Fuel pump monitor shows no power / Secondary fuel pump circuit open to PCM, or somthing like that. I have an adjustable fuel pressure regulator and I have to run it around 50 psi to get it to run smoother. Runs fine at wide open throttle, but around town It drives me crazy with the chugging. How do I fix this?? Thanks for any help