[OldChevy1954]

My 72 K20 has a something unusual happening all of a sudden. I replaced the speedo with an LMC unit a few years ago and it has worked fine. Accurate too since I put the right gear in the transfer case.

Now it's approximately 15 to 20 mph off at higher speeds. Sometimes its as high as 40 mph too fast.

What could be going on here?

Thanks.