[Mookster]

Intermittent problems are a pain in the butt! Don't ask me how I know.

Don't throw parts at the problem. Diagnose the problem not the symptoms.

Look for common issues when the vehicle stalls, speed, idle, braking, RPM ranges...

That being said start simple.

1. Exchange the fuel pump relay with the ac relay and see if this is the issue. Clean the fuel pump relay connections with a small round wire brush. Replacing the fuel pump relay is not a bad thing anyway.
2. Check the transmission to chassis ground strap. Clean the connections at both ends.
3. When the car doesn't start do you hear the fuel pump whine? (key just past half but not starting the vehicle is a good test to listen for the fuel pump whine). If there isn't a whine electrical is most likely the culprit
4. Old spark plug wires can be a bad thing. At night start the vehicle and see if you see arching off the spark plug wires. Mist a little water on them if needed. If you see arching, I suggest replacing the spark plug wires. Search other threads for recommondations if you need to replace them.
5. Permatune boxes have a bad wrap when they get hot. FYI. I would suggest going back to the Bosch CD unit or exchange one with a friend to see if this is the issue.

Starting point. Keep us informed. Good luck.