What Else Could It Be?

[Mytrucksachevy]

I'm at wits end with a buddy's truck. I hope this is the right forum for this post. I'll keep it short and sweet.

Truck is a 93 GMC 1500 with a 4.3 TBI

310K on the truck but only about 20-50k on the motor (barely got it broken in, I guess)

New trans last year.

The engine dies and the injectors do not pulse.

Fuel pump primes ok and there is over 1/2 tank of fuel in it.

Problem started with intermittent dying. He replaced the fuel pump when the truck refused to start again. Still wouldn't start. He replaced the regulator inside the throttle body and both injectors. Fuel filter was also replaced. When I came over, we put it back together and it ran fine. Drove around the block and died again. I tested for spark and it was sparking. I tested the injector harness with a noid light and got no pulse. Then, for no reason, it started pulsing and the enging tried to start. I plugged it back in and we drove the truck back home. I removed the module (thinking it drives the injectors) and the engine computer. We tested the module at the parts store 10 times or so...all good tests. So we bought a computer. Carefully changed the PROM and put it back together. Truck fired up and purred. It drove fine all night and then after 1 hour or so, randomly started to die. It fired up again and drove home, but now he tells me the injectors do not spit fuel, although I have not tested them with a light. Pump sounds like it is priming.

I've never had this much trouble diagnosing a vehicle before. Any help is appreciated. I have used forums to help on my other vehicles, but my '07 Chevy is still under warranty. Hope you can help.