Stalls and Won't Restart

1994 Pontiac Bonneville, when I drive for long periods of time the engine will stall out. It will typically restart in about 15-20 minutes. Mechanics can''t figure it out.

Has it been determined if the reason for the stall and no start is because of a loss of spark, fuel pressure, or injector pulse?
Depending on if the car is loosing fuel pressure, fuel injector pulse, or spark, makes all the difference in the world as which way to start looking.

Answer:

Of, course, these things would need to be checked as it is happening.
A loss of fuel pressure can be a fuel pump, or a bad ground.
A loss of spark and injector pulse could be a crankshaft position sensor- which is common to fail when hot, or a computer.
A loss of just spark can be an ignition module.
Need to find out what is missing first.