If you go 4x4 you get 3.73 rear axle ratio and the tow rating goes up to about 7000 lbs.
The new 4.3 is going to make a great Tow Vehicle for many folks. With its TQ rating over 300 lb ft.
If you all have not bought a truck yet I would strongly suggest checking out the Ram 1500 with the new 3.6 v6. You get the Amazing 8 speed and with 3.55 rear axle ratio you get over 7000 lb tow rating. And still get 23 MPG empty.
But, with your trailer any of the new 6cyl half tons will do more than fine with the tow packages.
Good luck in your decision and welcome to RV.net
Thanks!
Jeremiah