Your problem could totally unrelated, but I had a chevy silverado truck that would die when running. and just like you i replaced the coil,the distributor cap & rotor and nothing. finally after troubleshooting further it turned out to be the wire harness on the ignition switch. what happens when you crank the ignition....there's a wire that sends the voltage to the coil and in turn to the distributor that delivers the spark. Hope this at least helps you troubleshoot further, Good luck!