All of the guages on my instrument panel are working great except the Tach. 90% of the time when starting or just driving the truck the tach will stay at 0 or go to 6000 (full tach) and just stay there, sometimes it will lock up it different positions but never move unless I turn off the key and turn it back on. After turning the key back on the tach will still lock up again. Any help would be great thanks