my speedometer has a tendency to go whacky, but resets its self when truck is restarted several times.runs good for awhile then acts up again, could this be a speed sensor?
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This is very common on the 03-06 GMs. The cause is the motors behind the gauges are failing, they all go out eventually. You can get it repaired here - www.drspeedometer.com and there's a DIY guide here - www.howtorepairmyinstrumentcluster.com
thank you!