Grimm, this is a pretty old thread. May or may not get a response. You have a very nice truck. What is your current transmission and transfer case? Also, what gear ratio do you have in the differentials? From having owned a '73 F100 4x4, I know there isn't much sound proofing in these trucks. Noise control will probably be an area you'll need to address. The 4bt isn't quiet. With the proper OD transmission and right differential gears you could expect fuel mileage in the low to mid 20's. My old F100 was stuck on 13.7 MPG city or highway with its 360 V8. Rarely ever varied.