93 Pontiac Grand Am SE Overheating without notice

I have a 93 Pontiac Grand Am Se 6 Cylinder with 94,731 miles on it. Just yesterday I was driving home in Heavy traffic and later noticed my temperature was reading a little before the red marking but would not go any higher but slightly went down a bit. I checked all the hoses and checked the Antifreeze level everything checks out fine. The Antifreeze level still reads at the full mark. My car has idiot lights on it and didnt say whether or not anything was wrong. Im supposibly bringing it into the shop soon for a tune up to get new spark plugs and have the intake cleaned out of any grime. Otherwise the car checks out fine netherless this is the 1st time ive ever seen it overheat at such high temperatures reading towards the red marking. My Air Conditioner has been acting a little weird as well the air turns cold to very warm then all the way back to cold then warm again. I would have no idea if this is attuned to the car overheating or not. My A/C is always warm the only way to get cold air is to put the control on Max Air instead of A/C.