1. What is the difference between a Chevy and GMC? As stated - trim.
2. Love, It is ok, or hate your Chevy/GMC? Love it.
3. I am looking at 2010 - 2013 models. Any difference in those years? One year better than another? I would assume the later the better? The later model year you get, the better the emissions system will be (more "bugs" ironed out). All the major manufacturers have increased the GVWR/payload ratings as the years have passed. My 2013, after scaling loaded, has about 3,000 lbs. left on the rear axle for pin weight. Earlier trucks had less.
4. I am towing around a 34'/9,000 pound TT. For those towing around the same (TT or 5er); what type of MPG are you seeing? We get 19 - 20 on the highway not towing and 11 average (coast-to-coast/north-to-south) towing a 13,400 lb. fifth wheel.
5. Any other pertinent info you would like to pass on. You will not be disappointed with the DuraMax/Allison combo for towing. Pay attention to scale weights, payload, brakes, tires and hitch setup.
Rob