Issue with rMBP Nvidia GT 650M

Question

I think I'm having issues with my rMBP video card.
I'm getting terrible performance while playing games that were fine in the past. For instance, playing in WoW on OSX I could get 60 FPS on high settings before, now it's like 10 FPS.
It's a bit hard to validate it's the video card in OSX, because I can't find any tools to monitor the GPU. I've updated all the drivers for the video card. I've ran the Apple Hardware Test and it says everything is fine.
When I load Windows 7 in Bootcamp and run the program GPU-Z to analyze the video card, it shows the video card behaving strangely. After about 1 minute of the game, my GPU Memory Clock jumps back and forth from 1000 MHz to 200 MHz every 0.2-0.4 seconds. The GPU Core Clock does the same from 720 MHz to 270 MHz. The memory controller load is all over the place too from as high as 70 to a low of 20.
Anyone seen anything like this? Anyone know of a program to monitor the GPU in OSX?
I'm going to schedule a visit to the local apple store, but wanted to have as much info before I go.

Answer 1

Thanks. I've noticesd another detail that might help:
After doing the steps I mentionned earlier, the HUD colorpicker, the smooth zoom and the "red" brush shape that shows how hard the brush is, are no longer working/displayed.
Maybe the rescaling stops some GPU enabled features of the interface, thus leaving more "power" to the painting tools?