I have a 1994 4.3liter V8 Chevy Caprice. Sometime the car will start and drive fine with no problems. But most of the time fter I have been driving it for 20 mins or so the car will just shut off. The electrical system still works fine so I know its not the battery or alternator. After it dies it takes me about 10 mins to start it again. And then other times before I have even driven it and I come out to start the car it won't start. So far I've had the ignition module, distributor cap, rotor, wires and spark plugs replace. Any ideas?