My 2004 2500 Duramax overheats going up a 5% or better hill pulling 10,000 fully loaded 5th wheel. The rest of the time its fine, stays at 200. Once it starts getting warm it goes hot fast. My local dealer has tested everything they can think of. Truck has 22000 miles. Just got the 5th wheel, because I knew the Duramax could easily handle it, or should. Truck is stock. I'am haveing problems so I don't want to mess up the warrenty with after market stuff yet. I don't live in a extra hot climate either. Help?:help:

Do you hear the clutch fan engaging while climbing the hill?? Do a search on "overheating". I'm sure you will find others with similiar compliants.