Overheating in overdrive?
 

Ok, so yesterday I was on my way home from Portland, which is about 3hrs north of me. I was towing my 22ft toy hauler... and had it in OD on the freeway. Suddenly it started getting VERY hot.. So I pulled over and checked everything, radiator was fine, oil, everything. So proceeded home and kept it out of OD.. It did ok but coming up the steep tressel it got warmer than usual.. once the road flattened out it was fine again. Im wondering what the deal is.. I have done this route a lot and never had this happen...normal or not?
truck is 99 powerstroke, 7.3, 6spd, 8"lift on 38's.
I am fairly new to diesel's and any help would be appreciated!! thanks.

check cooling stack for debris if dirty clean..then check thermostat for function..then make sure coolant is in good shape..need to be changed ect. this should get u started hope this helps..

EGT gauge ?

Did you here the fan roaring when it was getting hot? If not, it could be a bad fan clutch. I think they are thermal on those, so it could be crap in front of the radiator, so the fan clutch can't sense the radiator getting hot. Or the fan clutch could be bad.