GTX 560 Ti Underclocking

When I'm playing a games mostly source games like TF2, Gmod, CSS my graphics card downclock to 400Mhz then jump back up to 1000Mhz, unless I drop down to 900Mhz core clock and even then it sometimes still drops to 400mhz. I have tested other driver versions like 296.10 and 310.90 with the same result, but 310.90 likes to crash with my OC and lock the card in 2D mode so I use 296.10. I also tried BF3 and it never downclocked to 400Mhz. Unsure on what the cause might be, here is a pic of MSI afterburner with my overclock. http://gyazo.com/3fb45001866d2f31dc8eda71bcd7b2db