rear diff ratio
That doesn't seem too unreasonable if you have 3.07, I dont think that it is 3.06. If you can tell me the factory tire size for your car, what size you are running now, I can figure out which one it is if you care that much.
Also, if you want to know. Climb under your car and look at the rear differential. if you look on the bottom left hand corner (drivers side) you will find the gear ratios. Make sure you also arent in third gear.
At 60 mph, turning 2100 is 2.41 gear ratio if that helps any. Typically mesurements from 60mph are easier to tell if you are in final gear (drive)
Hope this helps,