2002 Chevy Cavalier Cooling System?

I drive a 2002 Chevy Cavalier (5 speed) in Phoenix, AZ. Within the last year I've had the water pump replaced (about 1 year ago) as well as a second repair that had something to do with the water system but I can't remember offhand what, specifically, it was, just that it wasn't something that seemed obvious to me at the time (about 3 months ago - sorry I don't have more details, I'm trying to find that damned receipt). After the last repair, the car seemed to be running great. The air blew cold and I had no problems with the car overheating (which was a problem previously when in stop & go traffic). This morning while waiting to get onto the freeway the air conditioner started to sound as though it was struggling to stay on and the car seemed to be idling very low -- for a minute I thought I may have stalled. I checked the temperature guage and noticed that it was slowly crawling upwards. I turned the air off, and the temp went down as I drove along the freeway. On my way home I got stuck in heavy traffic. While waiting to exit the freeway (with the air off) the temp starting climbing into the red zone. I tried turning on the heat, but the heater worked as well as the air. The battery light came on and the car sounded like it was going to stall. I quickly got off the freeway and pulled over to allow the car to cool down. Since it gets so hot here, and we are under an extreme heat advisory for the next several days, I thought maybe the battery needed to be changed, that the car just wasn't getting enough juice to run properly. I took to Autozone where they checked the battery and said it was good. The Autozone guy said it was likely a problem with the water. A friend who works on his own cars all the time said it might be something with the fuel system. Any ideas?