98 Chevy Silverado speedometer

First thought would be bad electrolytic capacitor somewhere in the cluster, if the gearbox is behaving OK. The "capacitor plague" is usually cited as >99-07 but my experience says surface mount electrolytics from about '93 to about 2000 were actually the worst.

Otherwise, I've heard Chevys suffer with stepper motor failure in the clusters but not sure which years/models were affected. No direct experience since they're kinda rare in the UK lol