HELP---have fun guys.

I have owned 3 Dmax's and love that setup. Traded my last '10/1 ton/truck camper for an 08 F550 Super C. I am still towing 10,000# trailer, have an '87 Wrangler rock crwawler inside loaded with tools and a generator. The 550 handles the load as well as my '10 Dmax/3500. Both vehicles crew cab/4x4/diesel. I will say I am VERY dissapointed with the mileage of the 6.4 vs the 6.6 Dmax. The Chevy loaded with truck camper, loaded trailer, full tanks, food, clothes, etc would give me an average of a little over 10 mpg on my trips from the St. Louis area to Utah and back. My '08 F550 with same trailer, bigger tanks, additional fuel, all of our gear same trip gave me about 6 mpg. The power of the Dmax is better but the 6.4 is fine, I have no power problems. I actually pulled my Jeep behind my F550 over Cottonwood Pass this past summer. I was 100% satisfied with the pulling capability going both ways over that Mountain Pass. I am confident a gasser would have scared the hell out of my driving this route.