I have a 2003 2500HD single wheel with a Banks programmer on it and it gets 13-14 towing a 24 ft enclosed at 9000lbs running 70- 75 mph.

What gears are in yours? Mine is an automatic and has the 3.73 gears and that helps a lot.

I think the smarty programmers are what a lot recommend.

http://smarty-jr.com/