I bought a '97 4.6 used, and the previous owner went from a stock gear ratio (I can't find it off hand) to a 4:10 rear end. Changed the speedo gear in the trans from 25 tooth to 23 tooth and the speedo still is off 10%. Tire size stayed the same. What is the next step? Locally there is one and only one shop in town that can work on it and they want $200 to $400 to recalibrate it, but they won't give me a firm quote until after they work on it.