Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.
Have the speed indication checked while the fault is present, and give the technician the warm-up and restart pattern. Ask for testing of the speed-signal path and instrument display before replacing either.
Source: Original question and visible replies. Owner reports and other participants' experiences are distinguished. Next steps are editorial guidance for obtaining diagnosis or clarifying the reported findings; they are not a verified repair procedure or an independently confirmed component diagnosis.
Speedo Jumping around?
A 2001 Silverado 5.3L developed an erratic speedometer after about 30 miles of driving. Short trips were unaffected, and switching the truck off for a while temporarily restored normal operation.
Reported outcome: No confirmed cause or repair result was reported.
The reply described a possible sensor, computer and instrument-motor signal path but did not verify this truck's design or identify a failed component.
