It really sounds like a heat problem?
Being an old electronics guy in the Army my best friend for thermal problems was a hair dryer. Get the car completely up to temp. then start pointing it at the electrically controlled componets one at a time and see if you can put it in the "crappy mode" with the heat gun ? Spend some time around the computer, they are filled with componets that can become heat sensitive. But don't get anything insanely hot ! Just enough to simulate a fully hot motor on a hot day. It may not work but at least it won't cost you anything ? Well ... unless you don't have a hair dryer ?
