Miked_md,
This forum is seldom stumped! I think we should give it another week or so before officially declaring Stumped, but it might go that way.
You may have to validate your 1:4.08 diff ratio by lifting the car, spinning the rear wheel, and counting the axle rotations and drive shaft rotations.
Perhaps an odometer from a different model car, with different odometer gearing, was installed when unit was serviced years ago.