FWIW: I just had a similar experience with my car. It would just shut off...like turning off the ignition. Which it was.

You didn't mention (or I didn't read...) what ignition your running, but I had some corrosion build-up on the pick up & star wheel in my distributor that closed off the air gap. I cleaned the parts and all is fine. I'm running an MSD Pro Billet and from what I've read on their forum, this is an acknowledged problem. Don't rule it out with your set-up.