Temperature gauge is fluctuating sporadically, and the car doesn't seem to want to go sometimes. I just replaced the thermostat and I'm still having issues.

Check your coolant levels. If the coolant is really low it can cause swings in the temp. readings.

By the sounds of this it will be the electrical connections on the back of the gauge

The cars performance coincides with the fluctuation of the temp gauge. And the levels were a little low after I changed the thermostat. But I have filled it since then. Could it be the water pump? Or maybe a cog in the system?

What are the actual temperature readings? What are your driving conditions when it gets hot? Does it run badly when the temp is really high? If so you may need a new radiator, t-stat, pump, belts and a good engine flush. It also could be a radiator fan issue. Not all t-stats are created equal. Look for one that has a large opening - some have a very small opening.

It runs bad and wants to stop running when the temperature fluctuates high. I installed a new T-stat, and the engines been flushed when I put in a new radiator. The belt is fine. I'm leaving towards bad O2 sensors. I'm changing one at a time right now.

Sometimes it runs fine during a trip, but begins to act up like it has been. Sometimes at the beginning, sometimes in the middle. Short trips.

Replaced the front O2 sensor. Still doing the same. What's your thoughts about the temp. sensor?

After all is said and done, the water pump is what was bad. Replaced the existing coolant with new. Runs good now. But unfortunately my temp gauge isn't working now. But everything else is. Thanks guys.

did you replace the temperature sensor?