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Can someone help..My speedometer fluctuates once I reach 65 MPH back and forth 5 miles. I have changed the speed sensor in the rearend. My truck is also a 2 wheel drive. Truck runs great just this problem. Any advise will be greatly appreciated.
You either have a bad PSOM, Speedometer Head or tone ring in the rear end.
You need to put it on jack stands and put a scope on the VSS signal coming from the rear end. See if the pattern changes while you hold the speed constant and the speedometer is jumping.
You could also use a frequency meter.