Years ago I added an interior trailer brake control but I doubt that would have any effect. Thanks for the info that the A/C is involved in temperature sensing. Will pursue that route. Fuel gauge seems to be working, now. ??Have you done any electrical/electronic mods on the truck?
Outside temperature comes from the A/C system, which uses that information to know when it's too cold to run the compressor. Fuel level comes from the sender in the tank of course. Not sure how much those two things have in common.