I just got back from a 2000 mile round trip from Portland to Tofino, over to Squamish, and back. Got 12.8 mpg with the Duramax towing the 5500lb, 25' Passport, even in 95 degree heat with AC blasting doing 65-70mph. The last leg was today, a straight shot from Squamish to Portland with one stop for Diesel and a few for dog walking breaks. Great trip, I'm not even tired. The old Tahoe would have beat me up on that trip, and only have gotten 9.8 mpg. I'll take that slightly harsher unloaded ride for confident smooth towing without having to think about hills. Plus, the exhaust brake means down is just as easy as up. It was nice that Diesel is cheaper than Unleaded in BC, too.