So after i wrecked the stang i paint it and redo everything but as im taking down the road i stop the gas and my MPH flies up to 100 and then back to 80 then to 90 and to like 65... This whole time im going like 20 MPH.. whats the deal???????????

 

sounds like either ur cable is messed up or ur speedo itself may be screwed mine bounces till i hit bout 40 then once i hit 60 the faster i go the slower my speedo is at 70 im bout 80 at 100 im bout 120