Originally Posted by KPMullen
It was a running fan clutch test. It only runs hot on inclines/hills. Cools off in seconds as soon as I stop climbing, on the downhill, level, or when parked.
Weird, it seems like you hit everything you need to. You replaced the radiator, the fan clutch is working and the thermostats are installed and I assume tested and correct.
On cleaning the cooling stack, I'm assuming you are 100% certain that there isn't still debris/dirt in there? I cleaned mine out with a pressure washer (safely) after I ran on 10mi of dirt road construction and started running hot again. Got out a lot - a LOT - but it was still running hot. Took it in to an Oasis Network (RV friendly) Freightliner shop and then had to steam clean it for 45 minutes until the water ran clear. THAT worked. Even though you got in there to swap the radiator, could it be possible that there was more gunk in there by the other coolers?