Frame Rate Drops!

Hopefully I'm posting in the correct forum/thread. Hi TH people. So I've had a 550Ti for about 2 months and it was running perfectly, (I mainly play StarCraft II) And one day, these extreme, horrible, FPS drops occured. If It helps, I'm at manufacturer recommended bios OC @ 4.0 GHZ, and the GPU was manufacturer recommended bios OC at 1400 MHZ. I would get about 150 FPS to start out the game, and as more units appear, fps slighly lower as usual, but sometimes, the screen would freeze for a split second, and the FPS go below 30. It says there for about 3 minutes, and when it goes back up, it only goes to 60-70's. I recently got a GTX 650 and to test I downclocked back to 3.4ghz and no GPU OC. I still get severe FPS drops. Please help.

Thank you, Player