Well , all the things I would have recommended are already done by you or advised by the competent people we have here. So I think it's time to look somewhere else for the heat. I would disconnect the tranny lines from the rad and put a stand alone tranny cooler on there. At least by doing that you have 100% eliminated any chance of it being something other than the engine itself.
BTW what gears you got in that ram. I suspect it's somewhere around 3:55 , Just wondering if the engine is winding a little higher and the water pumps are cavitating the coolant and it's not circulating .