2001 dodge cummings 5.9 has quadzilla w/ adrenaline. My truck has been running good until i pulled my 24 ft 5th wheel camper up in the mountains and it started running hot, alot hotter than usual (215-220). I pulled over and let it idle and opened the hood and it cooled back down. I started back up again and i done it again, at 45 to 50 miles per hour up the hills...once i speed up it cooled back down...I have stock exhaust straight pipe and air dog fuel pump, and afe stage 2 air breather, but do i need a bigger exhaust or what could the problem be......

 

Moved to the Cummins section for you...

 

I'd be looking at replacing the thermostat and checking the radiator for debris.

 

220 is about where the clutch fan locks up. dont be afraid of a little RPM while pulling also. Like RA said checking the rad and changing the thermo aint a bad idea, new coolant would not hurt either. In the hot summer pulling a boat up a big hill my rig will get to 220 but then the fan comes on hard and it cools down. I run mostly water in the system, about 4 parts water to 1 part antifreeze.

 

I'm gonna bet the back side of the rad by the fan is plugged with oil residue from the blow by bottle... Clean it and problem solved.