I tow with the combo in my sig. I usually plan on 12.3 to 12.8 pulling my TT. Loaded weight on the TT is usually apx 8700 pounds with out water. I know that the 2500 HD diesel is quite a lot more expense to purchase and maintain. I have pulled with with the half tons all my life and never saw much more that 8.5 mpg. Will they do the job, absolutely if set up correctly. My tow vehicle is also my daily driver I get 14 - 15 mpg city driving and 19 - 22 mpg highway. The half tons were fine with me until I started destination towing of 800 plus miles and the wear started to show on the drive train.
Irregardless what you pick in a TT, be sure the tow vehicle is capable of handling the weight.