Car starts and runs great until reaches operating temp. Then backfires and dies.

What is your question?

I have had this car at 2 dealers, 3 shops and my step father (With 40 years Automotive experience) have all tried to find the problem but so far been unable to. The engine is a brand new crate motor from Ford. It has about 25k on it. Everything else has been replaced from the supercharger to the plugs. Etc... The car has always run perfectly. The general consensus now is that as the car was in a minor fender bender some years ago where the right front fender had been damaged and replaced that the wiring harness from the engine to the computer might be damaged? When I say that everything else has been replaced, I mean everything! The dealers have all had the vehicle in their possession for days on end, hooked up to their computers, and as of yet been unable to figure out the problem. We are all at a loss. Any ideas?