I tow with a Crew cab '00 F-350 Powerstroke auto 4x4 on 315/75r16 bfg's and we got 15-16mpg going to Daytona with 5 guys in the truck, a bed full of luggage, pulling a 18ft trailer with 5 bikes. The truck is as solid as they come and im a Chevy guy, the only down side is the trans which is going to Hardshift next month But its got 250k and has been to Florida 4 times this year and VA beach once.
I also wanna add that while getting 15-16mpg we made it from Marysville to the Florida welcome center in 12 hours including stopping for dinner and fuel etc