1992 Chevrolet Astro fuel pressure problem

1992 Chevrolet Astro van. I have a starting problem that suddenly appeared. The fuel pump runs sometimes when the ignition switch is turned on (for 2 seconds, to prime the system), and sometimes will not. A pressure gauge at the fuel port shows 51 PSI after the pump has been run (after priming cycle); 59 PSI while the pump is running. (Engine off). To get the engine to start, I tried bypassing the relay (sending 12 V through the 'prime' connector under the hood), and it started, although with difficulty and several stalls. Once the engine is running, the fuel pump relay will make contact and I can release the starter switch I used to send power to the priming connector. The engine will refuse to fire the fuel injector until I force the pump to run (which boosts the pressure to 59 PSI). Very strange. I'd replace the regulator next, but it's sold with the injector assembly and it looks like they built the van around it! A flow test with a pressure gauge (again, using a wire to send power to the pump) showed what I though look like good flow with a constant 51 PSI. There seemed to be air passing through the clear bypass line. (The gauge reads 1/2 tank, and I'm certain it's at least1/3 full. The book I bought says 'approximately 58-64 PSI' is good. How approximately? HELP! I'm from the old school - 5-PSI mechanical fuel pumps, and looking down the carburetor to diagnose fuel problems. Do the drive train control computers pack up in these trucks?