I am about to change from 3.55 in my '99L to 4.10. There is a 13%
difference which will affect speedo and shift points. I think that only two options are selectable in the program, 3.55 or 3.73. Does
anyone know if there is a choice for wheel size. I think that if 17"
wheels are selectable, the speedo and shift points would be close. Any info would be appreciated. Thanks.

 

No wheel size option in the existing Ford programers for the Lightning, only a single gear selection. Chip can be adjusted to compensate for incorrect reading.

 

Chip can be adjusted for it. I had it done. Although I would not suggest the 4.10, I would go with a 3.73, I am fixing to put mine back in. I actualy went slower with the same 60ft time with the 4.10, plus the gas mileage sucks. Although from 80 to 140 the truck pulls very mean like.