How many of us are there? Owners of Dodge based RV's?

I don't know too much -- but just an idea
Do you have a external transmission radiator.. Not too spendy but it sounds like its the hills not the heat.
Throw a 12v fan on top of that (as you may not be moving too fast to get the radiator enough air).
I live in Minnesota so don't listnen to me. I do think the transmission radiator is fairly common though.
PS - Are you towing anything? if so drop and follow through the hills.

Right?