I had an '07.5 which is identical to an '08. I owned it for about 40,000 miles and the only problem I had was leaking trans. cooler lines that were fixed under warranty.
I got about 19 mpg empty on the interstate, around 11.5 hauling the 11' TC.
This truck was a 3500 SRW reg cab 4 x 4 with almost no options. It weighed 6,800 with me in it and full of fuel. That leaves 3,100 pounds until you hit the GVWR of 9,900. With my camper and the family I weighed in at 11,140. I did have airbags and Bilstein shocks on it.
I only sold it to get a crew cab. It was tight with me, my wife, our 54 pound dog, and a car seat for the little boy all in a reg. cab.