Thanks all for the replies!
I guess one other thing that concerns me is both times this happened was while towing, but ironically both times was low RPM. First time I was at about 65-70mph on a flat highway. Second time was on a 35mph road coasting when I felt the sudden shift into 4th. I always use Tow/Haul. Camper is about 9k Lbs and the truck is a 2500 with 6.4 and 4:10's so certainly not pulling too much. Once it happens while towing then it continues to happen regardless. Not sure if the towing part is a coincidence or if it is a contributing factor. Either way it's frustrating sitting here typing this when I should be on the road right now.
Thanks again all!