I could be off-base here as I haven't had to repair this issue myself, but I believe the TIPM could be a suspect. As long as there's no wiring damage, the TIPM is probably where I would be looking next. Unfortunately it's an expensive part to just shotgun repair as a used one is $200+. There's a rebuild service that offers used ones at that price and they also understand it may not be your issue, so to save you the full cost of a TIPM replacement they will allow you to convert to a "rental" at 25% of the cost as long as you return it to them in a short time period. Not trying to advertise anyone's business here just mentioning it as an option.
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