I love mine, 17,500 miles, approximatly 7000 tow miles. 11.5-12 MPG towing and 18-20 solo.
Ford techs say they have seen them in the service bays but only for oil changes! I did have to have the NOX sensor replaced, but other than than that, no other problem(s).
Ford Truck Enthusiasts have a great 6.7 forum.
http://www.ford-trucks.com/forums/forum205/