My trucks speedometer read about 12-15mph too fast at 60mph it would read about 78. I checked every ground, wires, connection, replaced entire cluster with a 120mph unit and it still was the same with no resolve. I went to the junkyard and grabbed another gauge cluster out of a 98 suburban and turned on my phones gps and it is now 99% accurate. So if your trucks speedo is off the only solution is to replace the entire cluster. Its easy to swap your odometer into the new one.
Hope this helps.
Hope this helps.
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