speed sensor

What is the difference between Differential vs. Transmission Speed Sensors? I have a 2003 KJ Limited with the 45RFE transmission. Does it use both? My speedometer works after the Liberty has been parked for awhile. It continues to work at highway speed for about 5 miles then jumps around and...

My speedometer is not working. Has anyone had issues with this before that they could share? Autozone gave me a speed sensor but the one they gave seems to look like it actually goes inside the transmission. Codes also show that there is an issue with the speed sensor.