Starting trouble

I have a 94 Jimmy with the 4.3 Vortec(fuel injected). The problem is that sometimes it won't start, it will turn over with no problem but won't start. If I jump it with another vehicle it will start almost instantly. I put a new battery in it and had the alternator checked and was told it was okay. Then a shop said that it wasn't getting enough fuel pressure to start and that the pump was bad, I changed the pump and still have the same problem. Does anyone know whatelse it could be?

does it run rich...idle rough?
Poor gas milage?

Sounds like it needs a distributor cap, rotor, wires, plugs, etc.

does it run rich...idle rough?
Poor gas milage?
It idles rough when I start to put a load on the electrical system(ie. turn on the heat).

Sounds like it needs a distributor cap, rotor, wires, plugs, etc.
This is actually the next step that I have planned, plugs and the module under the distributor cap.

Problem solved, it was the fuel pump relay located on the driver-side of the firewall. The connection was bad so we cleaned it up and it has been fine ever since. I will be replacing it within a week or two just to be safe.