Gmc g20 van stalls when hot

I have a GMC G20 conversion van. This summer when it was hot it would stall after it was running for 1/2 hour or so. It stalled at an intersection, I could not restart it. I waited 5 to 10 minutes and I could then re-start it and it was fine. Also when hot it will very quickly loose power, speedometer will go to zero and then back. Then the engine will stall. Seems like it is an electronic issue. This has happened almost every time when it is warm. Now that it is cold I have not had the problem if I don't drive very far.