my experience is 2003 Duramax, no chips, 11-12 pulling a Sunnybrook 35ft fifth wheel fill to the gills. I would like a stronger engine for the mountains but I am not willing to put up with adding some additive to the fuel every 10,000 miles or less on the new ones. I do worry about taking it from Boston MA area to Montana, I fear if something goes wrong I will be out in no where and be at the hands of crooks. Here we have a great diesel mechanic. Diesel fuel is harder to find, you cannot just pull over and get filled up like with gas is the only downside other than mechanical costs. A oil change can be over $100 but lasts longer than gas engines.