Most likely your problem is back at the vehicle speed sensor on the rear end. First check the connection and wires since they are prone to get knocked off or broken over time. If the ABS light has been acting up, that's a sure sign the problem is back there. You could also have a problem with the connector at the back of the speedo head but I would sure check the rear end first. The connector is in the middle of the back of the differntial cover right where the rear torque bar crosses it. Make sure you have the car secure and don't try to jack it up with the tire jack to do this.