Tach Reading 1k Too High

[kupcar]

Hi, Anyone have a problem with their tach reading 1k high? It will do this on start up and it will read high for an unspecified time, then drop to correct reading. I'm pretty certain my grounds are good. Just replaced the ground to transmission. The car is a 76 930. It won't bounce around, just reads consistently high. Voltage regulator? I was planning on having the alternator rebuilt because it's original and I think the bearings should be replaced. Thanks, Jeff