That is a large error, what has been done to the rig, like tires, or transmission replacement etc.
It has to be something else because I have owned this truck for ten years and this just. Started 2 years ago. I have the size tires on it that it came from factory with and have not changed transmission.
Ok so either there is a vibrational pulse from the speed sensor that the speedometer is picking up on or the stepper motor is going bad on the speedometer. A live data scanner would be able to read the speed sensor so then you would know if it was the sensor or the stepper. But if you just want to take a chance replace the speed sensor and see if that brings back to normal.
OK thank you very much.
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