This my first 3/4 ton truck. Now have 9000 miles on the clock. I have owned about ten 1/2 ton trucks over the last 40 years. I have owned mostly Ford trucks. GMC has really done well with this truck. It is the 6.0 gasser. I haul a travel trailer and perform routine around the house hauling. The powertrain and load performance difference between the GMC 1500 5.3 and 2500HD is huge. I get better gas mileage pulling a trailer with this truck vs. my 2008 GM 1500 5.3 gasser. I have been getting 17mpg on the highway without a load. 11 mpg pulling a 7000lb trailer on the highway. I believe the GM HD trucks are the way to go with either 6.0 gasser or the Duramax / Allison combination.
Recently purchased an 09 GMC 2500HD with the 6.6L Duramax diesel 4WD. Came from an 08 Toyota Tundra 5.7L and the GMC can not only haul twice the weight and tow 5000lbs more but it also rides smoother when empty. It returns 20mpg unloaded on the highway and the engine note is just enough to remind you that you're driving a diesel but quiet enough to be mistaken for a gasser. The interior is also a nicer place to be than in the Toyota, with more style and materials of a slightly higher quality. The Allison transmission is very smooth and always shifts at the right times. Test drove against the F250 and found the GMC a better all rounder, that stopped and accelerated better. Payload equal.