After 105,000 miles, I have my first real problem with my 2000 GTP. When I punch it, the car falls flat on its face at 4000 rpm---scanner shows that it goes crazy lean. Fuel Filter is new, and about 500 miles ago I installed a Caspar Fuel Pump rewire kit. When I attach a fuel pressure gauge and cycle the key on and off 3 times, I have 40 psi with key on, then key off and it slowly drops---after 15 minutes it is down to 32.8 psi. This car has 2 fuel pump micro relays--14 and 15 (F/PMP SPD CONT).
When I crank car, I have 42 psi at idle. Disconnect vacuum from regulator, I have 52. Turn off engine, gauge drops immediately to 33 psi. After 15 minutes, it is down to 20 psi.
Could I have a bad high speed pump relay, trash in the tank, etc. ???? Any thoughts or suggestions are welcome.