Well I just got back from my break-in run on my truck. I had 1,500 miles on it and decided to hitch it up and work it. Put on an 11,000 pound Bobcat, trailer combo, and drove about 300 miles or so. And of course typical Montana mountains, a few steep grades needed to be climbed. The slowest the truck ever saw was 65 on the steepest longest grade. It kicked out of overdrive at 65, then proceeded to climb to about 70 and hold it. That was at least a 7% grade. Averaged 12mpg for the trip with blended fuel at about 45 degrees outside temp. I let a friend of mine drive on the way back who's been big into diesels for over 10 years. He said "Wow, this is the strongest pulling stock truck I've driven" This coming from a 2005 Duramax owner.