1990 c4 tach repair info please

I have a 1990 vette. The Tach reads about 3k hi. (shows idle at 3700) According to the shop manual there is nothing to the tach exxcept for
a connection to the distrubutor and the electronic module in the distributor. I rebuilt the distributor this wekend. Rplaced everything with new. The tach still reads the same. Does anyone know of a place that I can send the cluster to that will can rebuild/repair the tach? I thank you for any info you can provide. Enjoy your vettes and keep the shiny side up!
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