My speedometer's been acting funny the last couple months, and its bothersome. It started last winter, I started it up on a really cold morning and the speedometer would wind to crazy speeds (90-140 mph, when I know by the tach and what gear, I'm only going 35-50 mph) ... Anyway, as it warmed up it went away for the day, and it did this on only the coldest days in the winter. Just recently it started acting funny again, but in a different way. Now it will start twitching +-5mph from what speed I should be going. I should also note that my tach works fine and I have never witnessed it acting strangely at all. Where's my most likely source of the problem.. the gear in the transmission, the cable itself, or in the speedometer unit? ... and which is the easiest to deal with?