Speedometer bounces, reads incorrectly at times, shows speed even when stopped.

Hello, It sounds like the vehicle speed sensor, connected to the transmission, and the speedometer are not communicating well. The signal from one to the other has to maintain continuity, and must be within a specified range for the speed at which the vehicle is traveling (or not traveling). If the sensor has failed, it can send erroneous messages, conversely, if the speedometer/instrument cluster has failed, the messages will be interpreted incorrectly. Just like all other electrical systems, they must maintain a constantly correct signal to work right. You will want it scanned by professional scanning equipment, and if the cluster is bad, you might be able to get it rebuilt with a warranty if the service is offered for that year/make/model. Let me know your questions, and I'll get back with you ASAP. If you prefer to have the vehicle diagnosed, you can view the list of certified shops in your area here: http://repairpal.com/chevrolet-within-10-miles-of-jefferson-city-tennessee-37760