Biggest mistake I made was not getting the diesel in my previous 2009 GMC 6.0 2500HD...besides the MPG's sucking wind, the first time I hit a short stretch of 6% grade towing 9500lbs, I was sick on how bad the truck was handling. I "hated" giving up the GMC, it had all the extras...just missing the diesel!
I owned it outright, sold it, bought a great conditioned 2005 Chevy (didn't go to 2007 or better as I didn't want all the emission junk and so forth) tow just under 12K loaded, awesome power, great MPG's and tranny barely shifts out of gear climbing hills. With a few simple mods, truck at 700 ft/lb torque (605 stock), can't tell much of a difference driving friends newer diesels except they do have better technology and bling!
Made no sense in planning our " weekend warrior" trips solely on flat land...6.0 gasser generates all the spec torque at 4500rpm, truck sounds like a blender, just not right!
In short, get the diesel...you won't second guess yourself on he purchase after the first long trip