1998 Pontiac Sunfire Need advice in a bad way!

My car is getting hot when at idle like stopping at a red light and especially when under a load such as going up a hill. I have tested the fan with a jumper wire and it runs, it doesn't kick on until the car is almost overheated though, I replaced the coolant temp. Sensor (that didn't change anything), I even heard something about unpluging it while the car is running to see if the fan kicks on (tried that, fan doesn't kick on with it unplugged) Put in new thermostat and that didn't help (I wish I could find a lower temp one for it than 180 degrees) today I took the thermostat out and tried it without it to see if that helped but then it got so hot it boiled over. I'm stuck on what it could be(sensor, relay, water pump, etc.) Does the thermostat have to be in it? I kinda thought maybe the cat. Converter could be clogged but not sure don't want to go through that if I don't have too. Hope to figurer out if its is something else under the hood first. It has a great heater so that makes me think its not an issue with the heater core. Not sure of what else to check or try.