My 2005 Monaco Diplomat overheats only going up hill. Had the radiator and CAC removed and cleaned in Denver, changed the filter, radiator cap and checked for exhaust leaks but she still overheats going up-hill, not on flat terrain. She has a 400 ISL Cummins with 62000 miles. I'm running out of options. Any technical suggestions based on actual experience with this problem would be greatly appreciated.