I just had my speedometer checked from a speedo shop and it is correct to 45mph then it goes like this actual vs/ car speedo 55/50 65/54 80/65 all mph. Also the cruise control accelerates and deaccelerates constantly making it useless to use. They did notice after 50 mph speedo needle jumps about 5mph and also my check engine light came on about 3 weeks ago and don't know if it is associated with the problem. Called dealer and don't have a clue. Speedo place suggested it my be speedo sensor. Any ideas would be a big help? Thanks, Jack