70 Duster keeps shutting off

Well I have checked out the bulkhead connectors on both sides of the fire wall replaced the coil, replaced the ballast resistors and the only think else I can think of is the MSD box itself the motor will just shut off and then after a few minutes of trying to start it, it will fire up again.So I am stumped I am going to try the simple test that they have for the MSD box but it will be hard to tell if it is one of the times it will start and run for x amount of miles before it shuts off.