I was chasing a stalling issue the first year I had the car on the road ......I had changed all sorts of stuff and it seemed like the issue was fixed....then it happened again.....turns out the "new" ballast was bad....jus sitting by the side of the road a few minutes was enough for it to work again.....replaced that and knock wood, no issues since.
Also, check the crimps on the wiring to your ballast, firewall, etc.
I had installed a Bill Evans harness and had found several loose crimps and one wire (big black one at the firewall) came off in my hands.