Im using Tunerpro and I can't seem to find where to change the gear ratio.
Is it programmed in the eprom or is it ignored on TPI?

 

There isn't a 'gear ratio' per say in the calibration. If the rear gear ratio is changed this will affect the N/V ratio values when using a stick shift. And may require a change to the TCC lockup tables with an automatic.

As for the speedometer and the ECM's MPH readings, that is done via the drive & driven gears for the VSS or cable in the transmission.

RBob.