Heelbilly,
We had a '10 Chevy 1500 CCSB, 5.3/6spd/3.42 4x4, towed ~7,200lbs here in Mi and never felt we needed more power. The biggest issue is payload as mentioned. We were up to about 200lbs over the GVWR of the truck depending on how we were loaded. That was with growing twin boys. That's why we now have a '13- 2500HD, which we then ended up going with a larger trailer.
With our '10-1500 we got about 16mpg overall if I recall correctly. We average about 13mpg with our 2500. And yes, my 2500HD is my daily driver.
Good luck deciding!!!