Hi All! I'm relatively new to the site and read alot more than I post. I recently purchased a 2003 Silverado 2500 HD 4x4 6L truck all is fine but the cluster. While driving the spedometer will occasionally start to jump around, while it does this the ABS and parking brake lights come on and the transmission will jump between 3rd and 4th gears. It will do this for about a minute or to then I'm ok for awhile. I've seen many post about stepper motors but those posts seem to mention a STUCK or DEAD needle and mine is always on the move. I'm thinking speed sensor? Also the last time I tried to get the codes read the mechanic could not pull any, no power nothing. Truck seems ok otherwise. Any opinions on speed sensor idea? I'm thinking of doing that first then stepper motors if sensor doesn't cure it, and ant ideas as to why we can't pull codes would also plenty helpfull. Thank you in advance.