After changing from a 3.73 to a 4.10 rear end I found that you can not alter the differential ratio or tire diameter fields on the PCM to correct the speedometer error that occurs. It appears that the PCM still looks at a valid Vehicle Data Field (mine is 2AEF 1629 FF57)and disregards the rest.

We tried altering ratios and tires all afternoon and the speedometer still read 10% low.

Did anyone out there buy a 2.3L standard cab, 5 speed manual with a 4.10 rear end? If so, I would like to try loading your code to see if it corrects the speedometer.

If you get a VIN # from someone with the set up you want, I can try and run the as built data and that usually has the codes to program the computer.

Cool!
Thanks,