My guess would be one of the sensors in the distributor. Have you checked to see if any codes are set in memory? I know the check engine light might not be on, but you never know... there could be one set in memory. Just jump the wires and count the flashes. If you got a crankshaft sensor that just stops the signal it will kill the engine. What sux is that your problem seems to be so intermittent that it will be hard to diagnose. I'd recommend checking all of your battery connections make sure they are all clean and check all your grounds. Clean and sand all of them. Other than that i guess you got to hope it just dies and doesn't start one day so you can maybe find out what is the cause.