Hmmmm....
Seems like you've replaced all the other culprits, so looking to the fuel pump sounds like the right direction.
You might try the fuel filter and ballast resistor first, but if you're still on your original pump on an 88, it's probably a pretty good idea to replace it anyway. I bought mine for my '88 at Autozone, but I've heard bad things about them since then. You might look at the dealership or maybe do a little research because I specifically remember reading that some of them were better than others.
Also, there should be some write ups on the fuel pump replace on this site. But here's my quick advice:
Undo battery, of course.
Have less than a quarter tank of gas.
Jack up the back to give yourself some room.
Get a brass punch (to avoid spark when you're hitting the lock ring)
Definitely don't pull the tank, which I think Haynes says to do.Just cut all the plastic ties holding the wiring sending unit. That'll give the the room to twist the whole thing up sideways and pull everything out.
Clean off the electrical connectors, esp. the negative. They corrode a little and keep power from getting there. Happened to mine.
Ummm... wear goggles. Gas in the eye sucks.