After a few hours, or overnight, when I try to start my 91 305, it will crank, fire, then die a few times. I have to give it some revs on the 2nd or 3rd try to keep it going. Once I do, it idles and drives fine. I have replaced the IAC valve, egr valve, rebuild the throttle body and fuel pressure regulator (stock spring), new ACdelco injectors. I can hear the fuel pump prime, but it doesn't prime every single time I turn the key on. For instance, I can't get it to prime twice in a row. If I turn the key to "on" and it primes, I can't do it again immediately, it won't prime again.

I decided to do a fuel pressure test. When I prime it, it shoots up to about 9lbs but falls off very quickly. Is there no check valve? When it running, it's at a steady 10lbs even with some revving. Video below. Any ideas what would be causing this?

Pinch off the return line to see if the fuel pressure increases. 9 psi is actually low it should be between 10 and 12 psi less can and will cause the issues you have. Did you verify the pump actually priming or did you just hear it? Chances are the pump is bad.
Have you replaced the pump? If so the positive and negative could be reversed pull apart at the pump and switch polarity.
If you have not replaced the pump, I suggest doing so. Definitely get a good pump I have had great experience with Quantum Fuel Systems https://share.google/C8THKImGRK2rI0PL9

hey there! Thanks for the response. I don’t know if you saw the video I posted, hope it’s in the right format. I know the pump is priming because when I turn the key to “on” before starting, the fuel gauge jumped to 9psi then quickly lost pressure before actually cranking it. After it starts it goes up to 10-10.5lbs and stays there.

I believe the pump to be original. At just above 10lbs running, it seems to be in spec but at the lower end. Could that still cause it? Or should I check a few other things before going for replacement? Not looking forward to dropping the tank.

I’ve had leaky valve seals since I’ve had the car and I’m wondering if they could have plugged up the cat. I heard a plugged up cat can cause difficult starts if it can get the exhaust gases away fast enough.