1999 Speed sensor problem

I have a 1999 Aurora that after driving long distance I get a Po503 Error code. after taking it to the smog shop the error is a speed sensor error. my speedodomitor get jumpy to the point that the cruise control will turn off. can some one tell me where the the speed sensor is and is it dificult to replace?

I have the same problem in my 1999 Aurora. I purchased the speed sensor at Autozone, but I don't know where it is located on the tranny. Have you changed yours and where was it located? email me at [email protected] if you have done so. Thanks