Transmissions are a complex piece of machinery and require maintenance and service like anything else. I wonder if your existing transmission fluid got burnt or scorched you can usually tell by smelling the dipstick and seeing if it has the burnt smell if it does the viscosity of the fluid is probably down to the point that it’s not doing his job properly And can cause premature wear of the internal parts. When I upgraded to a larger travel trailer I added a larger transmission cooler to my truck and a temperature gage to keep an eye on it. I guess the moral of the story is do not neglect your transmission there are more moving parts in it then probably the whole rig combined.
Happy trails Jay