When I bought my 97 F250 HD 4WD it already had a 4" lift and 35" tires on it. I thought the speedometer was a little slow but didn't pay much attention to it. I recently got new 33" tires and now according to my GPS the speedometer reads fast. The speedo says 40 and the GPS reads 36. I went into the PSOM and looked at it thinking the previous owner had changed the seetings. My PSOM reads E 08 6 and 856 CAL. So it appears to me it has never been changed since there is still 6 changes. Is it possible the truck has a Superlift Truspeed or something similar? Where should I look for the unit? Any other ideas? Please help me out I'm lost on this one.......

 

Anyone........please........help

 

HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles

 

Why spend money on stuff to do what you can do for free with the link in post #3???