I have an 06 HD crew cab 2wd 4.11 with 6.0. I tow a 6500 dry weight trailer plus goodies 10 mpg 60 mph goes down with hills. Also have an 06 Diesel crew cab 4wd with allison tranny 4.11 pulls gooseneck commercially 13/14 mpg 60 loaded. Had Suburban HD with 8.1 with allison tranny 4.11 11/12 mpg 65 mph or less. Towed Travel Trailer 6500 lbs great. Have Suburban 1/2 half ton with a 6.0 I put in 2.73 gears and beefed up rear to tow travel trailer. Mileage similar to others. 4.8, 5.3 and 6.0 are same family of blocks different guts. Just came back from Riverside to Valencia difference in 1/2 ton vs 3/4 for me was ride especially through crappy freeways in LA was ride. My trucks are harsher on me but most parts of country just fine that why I beefed up my burb.
So if up to me 6.0/8.1 2wd crew cab hd 4wd optional if in area you need it. If you need to tow more you have the capability. Pretty bulletproof just keep up on maintenance. Shifts down a gear on steeper grades but maintain a constant 55/60 mph depending on traffic for me. Hope this info helps a little
