Duramax and Cummins seem to have an edge on the Ford product. I have an '06 Duramax with 140k on it and haven't had any issues with it. As mentioned, the 3/4 trucks are set up for towing with brakes and cooling systems to match.
Mine has averaged 15.1 mpg all in since I've owned it, mixture of city, highway, towing, hunting.
