hard starting 1990 suburban

I have a 1990 GMC Suburban 2500 4x4, with a 350. I am having a problem with starting the truck. When I can get it to turn over, it will only run for 10-15 seconds then shut off. I'v replaced the fuel pump 3 times. After the second time, the truck ran fine for about a week, then as I was making a turn it shut off. I tried to restart the truck it ran for about 5 seconds the shut off again. I thing it was running on the fuel left in the lines. Replaced the pump (while doing so found out that the ground wire from the pump was not securely connected, Fixed that problem). Before replacing the pump the 3rd time I had the same problem with the engine shutting down after 15 seconds. I have a new fuel filter. I know fuel is getting to the injectors, (unhooked fuel lines, and can see a even pattern of fuel from the injectors). I put on a new throttle position sensor, map sensor, O2 sensor, coolant temp sensor, cap, rotor, coil, and plug wires. If its near the throttle body its been replaced. I can remember the check engine light coming on with a running lean code. When I bought the truck (Aug 2002 w/130k miles) I replaced all the vaccum lines. At this point I am starting to think this problem may be electrical and not so much fuel. Is it possible that a relay is causing these problems? I'm sure this a easy fix, I just can't figure it out. Please help.

Thanks

Check the wiring connector going into the computer. My brother had a similar problem with an S10 pick-up. We could wiggle the wiring harness and get it to run. Ended up putting in a used computer as the problem seemed to be in the computer side connection block. Also, the "check engine" never did come on, so I think that it was in the wire connection that goes directly to the throttle body injector.

The relay for the fuel pump is on the engine side of the firewall (up high)just right (as you face it) of the heater core housing. There are two relays on the 2500. One is for fuel pump and the other is for transmission. I'd start there and trace down all youre wiring.