I have a turbo back 4" exhaust with a flow through muffler and an edge evo set on tow mode. Now with the cold weather and ULSD i get around 15-16 empty. I only drive 12 miles one way to work so that doesn't help my mileage either. I had a 99 F250 same truck as my 01 except it was bone stock and i could get 19 to 21 going 68mph to work and back. That was in the summer though and no ULSD.