either can make it start like that. fuel pressure spec is 41-47, you can rent a tester for free at autozone. put a rag around the end to catch gas and turn the key a couple times to repressurize(dont start it) see what your reading stabilizes too. if it goes away your regulator is likely bad or you have a leak. if its too low you need to find somewhere to plug the return, could be pump if its low. if it shoots up its the regulator. if the filter is plugged the pressure will be low and if you start it and rev the engineor if you can tape it up where you can see it driving it will go down the more you romp on it.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock