I tow a 6000 lb Airstream and am very happy with the peformance. I have the 6.0 with a 3.73 rearend. I don't plan on getting a bigger trailer so I wanted to maximize mpg at the expense of a little more grunt. After almost three years and 25K miles I think I made the right choice. I get about the same as mileage towing (12 mpg)as I did pulling my 5000 lb Airstream with an Astro van but with much better stability, acceleration, and stopping power.
I especially enjoy the quadrasteer and the autoride suspension. It handles like a small car - easy to manuever in parking lots and the ride is quite comfortable. I also enjoy the 37 gal fuel capacity.
This is the best truck I've owned. I don't feel the need to change anything.