Tow Vehicle...

I have an Everest, 34', Fifth Wheel RV on order: Dry Weight is 10,500 Lbs... I need a good Tow Vehicle... I have been looking at the Ford and Dodge Diesels...

Since I will be actually Towing the RV only about 2% of the time, and the remaining 98% not Towing My question is this:

I know that no truck gets good fuel mileage while towing, so I'm not worried about that aspect... It's the remaining 98% of the time that concerns me...

The Dodge people tell me that I should get about 17 to 18 MPG with the Cummings Diesel not loaded...

Can any body tell me what kind of MPG I can expect with the Ford Diesel?