Just returned from a vacation to Myrtle Beach SC from Maryland. On the way down, transmission downshifts in Tow Mode became loader and more pronounced. When I took the transmission out of Tow Mode, everything operated as normal:confused: Up shifts in Tow Mode were normal and she maintained speed on hills. Was a hot day (95 degrees) and I tow a 12,000LB trailer. On the way home, again downshifts were loud, but she did fine on 95 (held 65MPH at 2,000RPM). But once I reached Virginia/Maryland (route 301) after 6 hours of towing on another hot day, the transmission would not hold speed on hills. It would not down shift, had to do it manually, but even then I was losing ground:mad: Service light did not come on, will have codes if any pulled tomorrow. Nursed it home and have an appointment at the dealer on Wed. Took it out for a spin 2 hours after unhooking the trailer and all seemed fine, no loud whine during Tow Mode downshifts and she hailed ass up the hills:D Always leave Juice Attitude set on 2 (tow), and I am due for a trans fluid change. Search forum, could not find this issue. Any advice would be appreciated.

Forgot to mention, truck has 148K miles on her and the transmission temp was about normal for the conditions (hot days).

Ok, got the truck back from the dealer, no codes, could not duplicate. Technican theory is the temp of the air incoming to the engine was too hot, which forced the truck to disallow downshifts and lock up the fan at max speed. Hope he was right....