Tee a gauge into the fuel line on the back of the throttle body and check the fuel pressure. I forget the exact specs but it should be about 15-17psi when running and hold good pressure for a couple of minutes after being shut off. My 90 was like a new truck after I changed the fuel pump. It would run ok, but not great and be hard starting sometimes. Another common culprit on these trucks is the pickup sensor in the distributor.