Speedometer drops to 0, gear shifts, occasional stall.

[ginsingtome]

Hey guys, i'm just starting to learn bout repairing cars. Just wondering if anyone can help with the following issue.
I'm driving a 94 Grandam SE V6.
When I drive around 60Kph or so, my speedometer occassionally drops to 0, when it does so, it feel like my car shifts gears to try to get the speedometer back up to 60.
On top of that, occasionally my car will completely stall and shut down with all my warning lights on.
When it does stall, all I have to do is turn off the car and start it back up and it works again right away.

Any thoughts on what could be wrong and how to fix it??
The ironic part is that when I bring the car into the mechanic, he/she can't replicate the problem.. sigh...

Thanks
Ed

[bmtphoenix]

Wheel speed sensor. Almost has to be.