Code p0715

[Justin-561]

I have been driving recently and my check engine light popped on. The car started shifting pretty hard and O/D light blinks when on the highway(50mph+). I went to autozone to get one of those free code checks done, and was givin a paper that says the following:

TROUBLE SHOOTING P0715

Definition: Transmission speed sensor circuit fault.

Explanation: Vehicle speed above 15mph while transmission output speed below 60rpm.

Probable cause: Failed transmission sensor.

So I bought the $15 part he told me was bad, but after looking around internet im not sure I bought the right one.

If it is the right part, me and my dad looked all over, and couldnt find where to put it. I've found one on the Rear end (pumpkin), one above the trasmission (looks nothing like the part i bought, looks more like a connector), and was told by a local ford dealership part salesmen, there is also on inside the transmission its self(looks like the one i bought, but has a gear looking thing on it). I'm a little confused on which one is actually bad..please help, thanks in advance.