I've been following this thread as I have a fairly new to me 2008 Denali that has been running hot (engine) while towing my 4500lb travel trailer. I've changed the water pump, thermostat, swapped the radiator for a cold case two core and hooked up the oil and transmission cooler lines, added customized radiator baffles (the OEM ones are stupid expensive) and added a Derale larger transmission cooler. When towing up local hills with the AC on and my family in the vehicle, the engine temperature will touch 230, the transmission temperature has always stayed below 190. It always seems to go back down off throttle and on the flat will hover around 210 to 215. One thing that made a big difference for me was swapping out the Denali grille for a standard Silverado grillle. But the temperatures hitting 230 still concerns me.