speedometer needle gone crazy

G'day, y'all...I need some help:
On my way to work noticed the speedometer needle fluctuating wildly (amid the 10 to 50 mph indicated range) regardless of the actual speed of the vehicle, the car continues to run smoothly and the rpm's are pretty steady...any help will be greatly appreciated...RC

2000 rodeo.

Check towards the tailshaft of the transmission, where the speedo cable leads to. There should be a nylon gear in there that spins the speedo cable. Maybe the gear is shot.
G/luck
Joel

Sometimes the cables on some cars can stick in cold weather if moisture gets in there and freezes...especially if the car sat for a while without being driven. Just another option, but rodeo02's suggestion is probably more on target.