I have a 2017 F350 dually that is doing the same thing however completely empty no trailer or anything. I had brought it to the dealership 6 times insisting that anything above 215 degrees was not normal as it states in the owners manual however they kept telling me my truck was fine. On the highway with cruise control set anything over 70 the trans would consistently run 232 degrees or hotter. The hottest I ever saw was 253 degrees but that time I was towing a 26' low boy with a 4 door 7.3L on it. I kept bringing it in because I had a 2012 6.7 f250 that with the same trailer with a obs 4 door 7.3L my transmission never saw above 208. They still tried to say it was normal. About a month ago I was cruising down the highway with cruise control set at 80mph with no trailer or added weight and the transmission was at 232 degrees then the transmission randomly downshifted to first gear and blew my drive shaft. The truck has been at the dealership for 3 weeks now and they put a new drive shaft in and they are still trying to say the transmission is ok. I almost got in a wreck because of it. All I have ever owned is Ford Trucks and I love them but this truck has been giving me a lot of trouble if anyone knows anything about this problem please let me know.