You may also want to look at Suburban and Navigator as a tow vehicle for that weight of trailer. Just make sure the vehicle has the capacity for cargo, people and TT.
A Crew Cab pickup will be comfortable up to a point. There is plenty of leg room in the rear seat even for 3 adults. I would choose diesel for the added torque for hill climbing but be sure to get an exhaust brake for down hill. The ride will be like a truck, especially when empty. The suburban/navigator will give you a better ride.
The chevy/GMC duramax with allison transmission is a great combination and seemed to be free of issues in 2007 or 2008. Some of the earlier years had problems.
Good luck in your hunt.