For what it's worth, we have the GMC Sierra K3500 4X4 (one ton) with the Duramax, Allison, and SINGLE rear wheels. It is an "everyday" driver going to work with me right now. It runs great, is VERY comfy (LOVE those heated seats), and pulls the Monty 3400 like it wasn't even back there. Just got to try it out in snow last week, here in the NW. 12 inches in an unplowed parking lot and it just "bulled" its way through (no trailer behind, though.) Truck with hitch in the bed weighs in at 7300 pounds empty (no cargo.) On the freeway empty I get 22 MPG. To work I'm getting 17, with the Monty I get between 11 and 12 MPG at 60 MPH. We looked at all three brands, and just liked the GMC the best. Of course, the dealer's quote was that the Chevy/GMC are pretty much the same, but at GMC they actually "tighten all the bolts"....ah, internal "friendly" competition.
As everyone says, it is YOUR choice. Our GMC/Monty are our retirement rigs (6 months and counting.)