Here is what I found. From what a buddy of mine told me, this could be the cause of a bad speed sensor. According to him, if the speed sensor is bad, the signal to and from the car's control box will screw up the trany shifting as well as the speedo. He says since it is magnetic, it works better when the car warms up.
Now, how true this is???????? I have mild to high confidence in his opinions. He does own a garage though.
Hope this helps.
