I have a westach temp sender and quage installed in my 01 HO.
I use Texaco mtx fluid. I have had the qauge set up on my truck since 5,000 miles. I now have 35,400 mi. I have kept a log on temperature on trips and loaded conditions. I have never seen anything higher than 165* with outside air temp at 100* and a heavy load (trailer & tractor) about 13,500 pounds. It usually runs around 150* if the outside air temp is above 70* with colder temperatures 55* down I regularly see 125* trans case temperatures. The oputside air temp seems to have a much greater impact than speed/load.