Are you running the 10 speed Trans?
I have a 21 TrailBoss 6.2L/10speed that I tow a 9k lb travel trailer with. last year trans temp in the summer got to 235 and was stressing me out. We just went out for the first trip this year, outside temp was in the 60s and the trans was running between 180 and 210.
Ive read AMS oil claims that their fluid reduces temps by 20*... IDK that i believe that claim, but I would love to get the temps down 20 or 30*