Here's the story:
Stock 87 TPI, no bolt-ons, Walbro 340 fuel pump installed last year. I have a fp gauge mounted on the rail, and it used to fluctuate around 38-42 while running. The other day, the car pretty much felt like it gave up comming in from a long drive(more than 1/2 tank of gas) and ther fuel pump was pretty loud. It stalled comming into the apartment complex, was able to restart the car, but it ran like crap. I was not able to give it any gas or it would stumble and die again. The fuel pressure gauge was showing a steady 31 psi on the rail. When I went to try to start it this morning, it had 31 psi still, after priming the system. I turned it on, and it seemed to idle fine. I clamped the return line with some visegrips and the pressure went to 34 psi. I disconnected the vacuum line and the pressure went up to 32 psi. While reving the car, I get maybe 33 psi at the most. Is this a fuel pump issue or a regulator?

 

disconnect the fuel line at the fuel filter and clamp off the return line. Check fuel pressure at the tank.

If it's low, then it's your fuel pump, if it's normal, then it's your regulator.