The ECM will not cause this. The gear in the transmission is what is doing this. There is a gear that has a number of teeth for the engagement of the speed sensor to send a signal to the ECM.
When the number of teeth is different than original, this is what happens.
The answer is to take it to a speedometer shop that will put an adapter on the transmission that will change the speed of the speed sensor to match the speed of the car.
Roy
Wednesday, April 15th, 2020 AT 4:00 AM