I am having problems with my speedometer with my Mustang. It seems to be sticking". Sometimes it doesn't move off of the zero and other times it shoots up to the 70mph zone, of which I know I haven't been going that speed. It doesn't do it all the time but it is becoming more and more prevalent. Here are some additional facts that may come in handy:
'95 Ford Mustang 3.8L
-automatic transmission
I recently came back from serving a mission in the Carlsbad area and the car was left at home for a couple of years. It wasn't driven very much, basically enough to keep everything lubricated, by my parents. Right now my Magellan GPS is serving as my speedometer. What suggestions do you have?

Thanks!!

TOWENS