I'm having a problem with my 91 Loyale, when I am driving around in normal stop and go town traffic the temperature sky rockets to just below the red overheating line on the gauge, but when I get it up to speed on the highway the temperature drops down to its normal operating temperature, which is about a third of the way up the gauge. I was hoping someone else might have had this problem, so I don't end up spending more than I need to fix the car since I am planning on selling it soon. I'm guessing it is a thermostat problem, but I am not completely sure.

when it get hot does the passanger side fan come on? how olds the radiator ? last time you did a flush ?

Check to see how many of the frilly fins of the radiator have fallen off and check the electric fan. If it isn't coming on, unplug the wires to it and check to see if theres +12V at the connector (this is with engine hot, not running, but in on position) If there isn't, check the thermo switch, wich is on the passenger side of the radiator.