I have a 2009 Denali and have had great luck too. I heard the 2014 Denali would be a new body style.
I had a 2009 Chevy 4 door Z71 with the 5.7 liter motor in it and man it pulled the boat like a dream. It was a whole lot better than the Denali. Twice I was on the interstate running 70-80 mph and would forget the boat was behind me. I always know the boat is behind me in the Denali.
Either way the gas mileage stink and so does the rear seats that don't lay down flat. I hope they fix the seats for 2014!