2015 Chevy 4x4 Dbl Cab 6.0L w/4:10 RE. hauls the Rockies with no problems. A little slower than those that speed by, but I'd do this one again in a heartbeat, and have two 6.0L in a row, traded a 2003 GMC at 214,000 miles for this one. Very happy with the power and the truck hauling our Lance at about 3000+ lbs or so.
It's never wanted to climb a hill it couldn't climb. And has been in some pretty crazy places ... We live in Florida now, but camp in the western states almost every year.