I had a 08 2500HD LTZ with a 6.0, key phase there is had.
Loved the trk hated the motor. That being said I own a enclosed trailer sales company here in Maine.
I have a trailer on it 85 % of the time. I also haul a 24ft plus the v, with 2 legend cars in it, 8000 ish lbs 15k mi a year. The motor had no torque, till you turned it 3500 plus (watch fuel tank empty) great power at rev none down low. It was great by itself, but a 1/2 ton would do better.
I replaced it with a 2010 2500 HD LTZ with a duramax, it gets WAY beter mileage WAY.
Gas trk 14-17 by itself, 7.5-8.5 towing.
duramax 17-21 by itself 12.5-15 towing.
That's my real world experience.
Bob W