2006 vs. 2011
I had a '06 GMC 4X2 2500HD, 6 liter gas motor with a reg cab 8' bed and 410 gearing. I now have a 2011 Chevrolet 4X4 ext cab 3500HD also with 410 gearing. The towing performance is mostly identical. The ' 06 was lighter due to it being 2wd and regular cab. Both averaged about the same mpg while towing the same 6200lb TT. Usually 8, 9 maybe 10 on a long straightaway. The 2011 likes to try and shift multiple times between 3,4,5, & 6 gear. Being able to lock out 6th gear is a plus while towing. The suspension of the 3500HD is a big plus in the towing game and is the only superior ability in towing over the '06. The marketing hype on the "new 6.0" gas motor isn't noticeable. Honestly, trying to tow more 6000lbs with a 6 liter gas engine is probably not a good idea. The lack of a turbo on the gas engine is a significant detriment. Running in a unloaded condition the 6.0 gas motor is good.