Remove the cable from the back of the speedo housing and pull the inner cable out, wipe it down and inspect it for any flaws, lube it up as you install it, and drive it again to see if that fixes it. More than likely that will be all that is wrong. Need to keep them lubed as soon as they start to act up, if you let it go too long it can strip the plastic gears in the trans trying to turn the cable.