Why is my FPS fluctuating in World of Warcraft?

Hey everyone. I just started to get back into World of Warcraft today after taking a month or so off. Prior to 4.1, the game ran like a dream, with next to no lag. Lately however, it's giving me some trouble. I can do most things just fine; walk, fly, summon mounts, scan the AH, etc... But whenever I try to queue up combat on the training dummy and other mobs, my FPS dips horrible. My latency is fine, consistent too, but whenever I start to fight, my FPS drops from its usual 60 to 15 or so. It's making the game unplayable! I updated my drivers, turned off addons, did pretty much all the obvious things. Is anyone aware of any similar problems or fixes? I have a 3.44 GHz Quad Core processor, 4GB RAM, and NVIDIA GeForce GTX 460. I'm playing the game on max settings, but also tried setting them to the lowest and the FPS drop still persists. Any help would be appreciated. :)