Truck is 4X4, extended cab. When towing our 22' trailer in Arizona, up substantial hills, truck gets overly hot (yellow check temp light 2x, red overheated light once). When I pulled over, the exhaust manifolds were red hot (like they just came out of the mold). Same hills with NO load, it runs fine and cruises up the hills at 75 MPH and the temp guage doesn't move. When loaded, whatever the speed, I don't let it go over 4K rpm's whether it is in third or second gear. Trailer is about 3500# dry and about 4900# wet. Trailer before was a pop up that was about 3500# loaded and the truck did not do this. It only does it when I am pulling the new trailer. Water pump and t-stat, hoses and coolant were done at about 132K miles. Outdoor temp seems to have little effect except for how quick it will occur.
Other than the condition above, it consistently (and since day 1) runs at a normal temp of just less than the 210 mark on the guage.