1988 GMC Sierra Pickup - Engine quits when driving

My friend and I have been working on his pickup for some time now and can’t seem to pinpoint the problem.

He will be driving along and the engine will quit as if the spark has completely been withdrawn - no sputter. If he lets it sit for a while, he is able to restart it again. He noticed that the battery light will flash every now and then prior to the engine dying. He also noticed that the engine will cough every now and then while he is driving at highway speed.

The longest he has gone recently has been 4 days without stalling.

We have replaced and reset the timing chain, replace the distributor cap and rotor, coil, fuel filter, alternator, and battery. We have checked the grounding wires from the battery and they are fine. We have looked for cracked or broken wires. The starter runs fine. The fuel pump sounds okay.

The only thing we can think of is possibly something in the ignition that shorts out when it gets hot.

There is also a nasty squeaking coming from one of the pulleys in the belt system. We can’t seem to identify where it is coming from but when we took off the belt and spun all the pulleys by hand, they seemed fine. The belt itself is in excellent condition. The A/C has been disconnected but is still a part of the serpentine belt loop.

Any ideas? We really need help. Thanks in advance.