Speedo Help - Yes I've searched :)

[Android04]

So after searching through 433 results I still don't have an answer...

So I have a 65 C10, 327, and 3 on the tree. Last winter I complete redid an all gauges cluster and swapped it out for my lights cluster. In the process, I also replaced the speedo cable and it has a brand new speedo in it from LMC. So ever since the install, the odometer works perfectly, but the speedo bounces slightly and once I reach 50mph the speedo will stick and not move again until I shut off the truck.

Thoughts? Bad cable? Or bad gear in the transmission? I have another gear from a parts 3 speed that I'm going to swap over next weekend but wanted to get your thoughts?