speed sensor

I have a 2003 Protege5 with about 106xxx miles, the car drives and shifts through all the gears just fine, but when I get to about 71 MPH the AT light starts flashing, (i can go over this speed and have, but weather I speed up, slow down, or stay the same speed, the result is the same) after...

Hi all. I have a 1.6l w. an automatic transmission. It has intermittent shifting problems like dropping out of O/D at freeway speeds and shifting hard in/out of gear during a full stop and just having issues shifting in general. A mechanic friend of mine believes that it is the speed sensor...