Is there a wire wound ceramic resistor attached to your motors & is the wiring connected to it? If it's there it should be connected into the circuit per Chrysler diagrams.

If it's not it may be possible to add a resistor to lower motor speed depending on how the motor is wound. If there's an electric motor shop in your area they should be able to take a look & tell you if a speed reduction with resistor or rheostat is possible. It often is possible.