Realilistic mileage with a fifthwheel.

For what it is worth, my truck (1996 F250, 7.3L diesel, 4.10 rearend, manual transmission) was getting around 10 mpg towing. This spring I made a few upgrades. All new 4" exhaust, eliminated exhaust particle filter on exhaust, removed exhaust back pressure valve, added a TS performance 6 position chip, and rebuilt the turbo (stock configuration). Now the truck consistently gets 12 to 12.3 mpg towing at 65 mph (11,000 lb 5'er) with the chip set on 50+ HP. Daily driving to work (250 miles per week) the truck went from 18 mpg up to 22.5 mpg (mostly interstate driving at 65 mph). I've tested different positions on tuner chip and it seems like 50+ HP is the sweet spot best mpg. I can dial up to 140+ HP with this chip for hill climbs if needed but so far 50+ is enough. Exhaust gas temperatures with the chip set at 50+ HP keeps the 7.3L in the safe zone.