All 4L60E's have it. The sensor clips to the transmission filter. The PCM alters shift points when the fluid begins to overheat, commonly referred to as "limp mode". Easiest way to monitor the fluid temp it is with a scan tool.

 

If they are equipped with a factory temp gauge where on the wiring harness do I splice into for a accurate reading. I got a 2000 jimmy slt

 

They are not equipped with a temperature gauge, only a sensor. The "gauge" is the scan tool. The sensor is a thermistor, a resistor that changes resistance with temperature. The PCM monitors the voltage, converts it to temperature, and alters the shift pattern accordingly, when necessary. You can monitor the fluid temperature with a transmission capable scan tool. Splicing into the sensor wire may affect how the PCM interprets the data, not a good idea.