Q: 97 Firebird engine getting too hot.

So my 97 Firebird has been having issues concerning the cooling system, as the car gets too hot in stop and go traffic, ESPECIALLY with the A/C on, which by the way takes a while to actually get cold, but doesn't ever redline. She doesn't get too hot while going at high speeds such as while I'm on the highway, but generally if I stay below 2000 RPMs the needle on the temp gauge begins to go over the halfway mark, which makes me nervous.

I was thinking it could be the water pump, as when I rev the engine/speed up when she's getting too hot her temperature goes back to where it should be, but I'm really hoping it's not the head gasket obviously. There were some external leaks, but after I put some stopleak in the radiator they've been gone from what I've noticed. Engine performance seems fine, as everything is except for the fact that she's just getting too hot...

My car has 130200 miles.
My car has an automatic transmission.