2005 Nissan Armada

Electrical problem
2005 Nissan Armada V8 Four Wheel Drive Automatic 7000 miles

I put my car on the Diagnostics machine its bring up a code of P0720
which says its an out put speed sensor. I have called the dealer to get the part and they state its inside the transmission and the sensor is $900 Im puzzled because the person that was going to change it said its next to the transmission? Im I ordering the part wrong? Also how much time do I have to change it I have been driving it like that?
April 14, 2010.

It's actually called the revolution sensor on your vehicle and it is located inside of the tranny.

Apr 14, 2010.