Intermittent Speedometer Operation

Your vehicle has the 4T60E transmission,and there is a speed sensor mounted on the transmission case that the vehicle's computer uses to compute vehicle speed,and relay it to the dash mounted speedometer.The best way to diagnose this problem is to first,hook up a scan tool that is available at automotive repair shops,and scan the vehicle for trouble codes first.Your vehicle probably has a stored trouble code along the lines of a Vehicle Speed Sensor (VSS).After pulling codes,go to the data stream on the scan tool and look at the VSS signal that the computer is seeing,and when the speedo acts up,and stops working,look to see if the computer is seeing,a speed signal.If the vehicle computer is seeing a speed signal,then it's probably the speedo in the dash gone bad.If the vehicle computer is not seeing a speed signal,then it is likely a problem with the speed sensor mounted on the transmission,or the wires right before it.So,to diagnose really requires a scan tool,with a data stream,or you could just have the speed sensor replaced,and hope that fixes it.The speed sensor is located on the passenger side of the transmission,only accessible from under the car,but where the pass side axle actually goes into the transmission,the sensor is directly above that point,and retained in the case with a 10 mm bolt.It has two wires going to it.Good luck.

No, there is no voltage at the speed sensor plug. Key on or off.
The sensor is a magnet and generates voltage to the PCM when the car is moving.
Check the wires to the speed sensor.
I had a brake master cyl leak, and thought it shorted out my Trans switch(neutral safety) so I replaced it also, and the speedo is still inop. Any help would be great.
Thanks