Speed Sensor-'98 Sunfire GT

[elysec]

I had the speed sensor replaced in my '98 Sunfire GT May 22/07. (because the speedometer would flicker and I couldn't tell just how fast i was going.)
Now It's doing it again. So I took it back to the shop and they said it's the speed sensor again. I was curious to know if they replace it AGAIN and it's not just a faulty speed sensor what else could be the problem causing this issue?? Wiring? Transmission? ....other..... Thanks!