If you do not already have the truck...I highly, highly, highly recommend a 2009+ 5.3L 6-spd. Few people are happy with the 4.8L. And the 4-spd auto is relatively dreadful compared to the 6-spds.
Towing any high walled RV is hard work on the tow vehicle. That's why we get 8-10mph instead of 20mpg at 65mph. It doesn't hatter if it weighs 5000 pounds or 10000 pounds. You are pulling two sheets of plywood through the air, the hard way! So you want some reserve power for the slight incline, or uphill freeway on-ramp.
