Was out of town for a couple of days. I am sorry, your symtoms fit the fuel pump perfectly.
The only reason for the fuel pressure to drop that drastically when you turn the enigne off is a fuel leak.
So is either draining back to the tank, a line leaking externally or the fuel leaking into the engine (a leaking injector, fuel pressure requlator, etc.)
How is the pressure on the pump you installed?
The fuel pressure regulator is fairly easy to check, remove the vaccuum line that goes to it and check for raw fuel, if it is present the diapham has a hole in it and the regulator needs replaced.
I did check for Technical Service Bulletins before my first post, but again with your description so closely matching a textbook failing fuel pump; none of them fit as well. There is one (#03-06-04-030F) that deals with drivability concerns and hard starts and lists codes P0171, P0172, P0174, P0300, P01174, & P0175. Is your check engine light on and can you have the PCM codes read? This TSB goes though the GM process for cleaning the injectors that requires special tools and GM top engine cleaner.
I only have TSB"s available to me in a ". Pdf" (adobe reader) format and have never neen able to successfully post those. Send me a private message with your e-mail address and I'll send you all the info I have.
One question; when you replaced your fuel pump did you replace it with a new unit or used? I ask this only for information. I have intsalled used pumps at customers request and have only had about a 50% success rate with them. About two weeks ago I help a friend put a used pump in his mothers 98 S-10 pick up and it took two returns to get a useable pump.
A few more Ideas, send me that message and i'll do my best ro help you out. Thank you once again for your donation, it allows the guys at 2carpros to keep this site up so we can all get on here and share ideas.
Monday, October 12th, 2009 AT 5:43 PM