Ok, now, I need to know if anybody knows whether or not the PCM changes the speed sensor signal before sending it to the speedometer. If it does then I need to know if anybody knows whether or not they make aftermarket speedometers that can be dialed in to read direct feed off the speed sensor.

 

The PCM changes a pulse count signal from the sensor to a variable voltage at the speedo. This voltage signal is also used by the cruise control.

Couldn't tell you about the aftermarket.