"Sounds" like a signal generator problem. It's inside the distributor (pick up coil)-aftermarket part available btw.
These can work off and on like you are describing.
PS Don't crank your motor for prolonged periods, over 5 secs. at a time for example, that can destroy the ignitor (300+ bucks). It WILL fire instantly when you lick the problem. I bet, your old coil is just fine too. <img src="/forums/images/graemlins/oink.gif" alt="" />

fast enough to beat its own shadow