Cummins N-14 getting hot

What rpm are you pulling the pass at?
I had a 500 it needed a good bit of air on long pulls 1600ish rpm.

 

Is the temp your coolant or oil. If coolant that is a little warm. Oil temp that would be ok.
Easy enough to slow down, Down shift and run higher rpm. That will help run cooler. Turn your a/c off and turn your heater on.
Good luck.

 

Not specific to your details, boiling point we all know is 212, under pressure it is higher. You are probably running at the ceiling of temp range. Running up a grade with your scenario, I would drop a gear and raise rpm to get around 1500.

 

ALL engines heat up when climbing long grades. It's the nature of an internal combustion engine when you work it hard, especially at the lower speeds climbing as there is not enough natural air flow to cool the radiator.
If it's a big enough hill, it's best to not run it all the way to the floor as fast as it will go. Better to let off on the throttle and drop a gear or two and take your time.
Personally I turn the engine fan on ahead of time, when I know it's going to come on any way, too keep it from getting too hot, then leave the fan on all the way to the top.

 

Being a 2000 it can be a lot of little things that add up ... Slight wear in water pump a bit of airflow obstruction aka bugs dirt ,mild corroision in rad .. I'd do like others say and run a gear lower where you can still accerlate easy that way your not putting all the power to it and it should run cooler

 

My fan clutch on my 379 wouldn't lock up, which wasn't a problem except idling and pulling hills. So I didn't idle, and I dropped 2 gears more than necessary. I had no problems so I could get home and fix it.

 

Replace the thermostat, is a maintenance item. How do you know if it only opens 90%? Speed more money in time testing it than to just replace it.
Make sure the cores in front of the fan are clean. Some require disassembly because you cannot get to or even see in between radiator, CAC, etc.
Water pump belt, hear a faint squeal at high RPM?
Check water pump pressure in block.