Steiner,
Good luck with your truck, mine was a 3500HD 15,000# gross payload. I liked the truck a lot, but I have been a Ford man all my life and I wanted F-350 crew cab. My 6.5 turbo had a 4.63 gear ratio in the rear end and it still got 18.5 mpg on the the road and 12.5 mpg in town. I thought that was pretty good since I weighed the truck on Cat scales at the truck stop and it weighed 10,682# with all my welding equipment I carried everyday. Pretty good mileage, but not enough power . Have fun.