Need help downclocking my 560 Ti.

Hey guys. Long story short, I am having problems playing Starcraft 2 with my 560 Ti (exact card here). The problem is every so often, my screen would flicker, and sometimes the game would crash. Through a decent amount of time, research, and testing, I came to the conclusion that the problem has to do with the fact that my card came factory OCed. Please trust me on this.

Base core clock speed should be 822 MHz.
My card came overclocked at 832 MHz.

I have downloaded MSI Afterburner and simply went to decrease the core clock to 822 MHz. (I should note that even though I set it at 822 MHz, the graph on the right shows that it is at 823 MHz, and I cannot get it to exactly 822 MHz.) I didn't change any of the other values, though the shader clock automatically went down from 1665 to 1645 MHz. Exact settings can be seen here:

The above settings allow me to play the game smoothly, but there is one major problem... the core clock speed goes back to 832 MHz during a game of SC2, causing the same instability problems described above. I have no idea what causes this, but my first guess would be the voltage? Keep in mind that I have never OCed anything before, so this is all brand new to me. I just got out of two games after SC2 crashed on me due to this, so I am asking here for help. After I finish writing this, I will try lowering the voltage about 10 mV, and see if that does anything.

In the meantime, I would like to ask you guys what may be the cause of my core clock speed going from my settings of 822 MHz, back to the factory settings of 832 MHz? Is there a way I can permanently set it to 822 MHz? Is it a good idea to lower the voltage a little bit since I downclocked the core clock? Any other ideas for me? Any other tips on downclocking?

Thanks for reading!

Computer Specs:
- i5-2500k
- ASRock Z77 pro4-m
- 2x4gb ddr3
- MSI N560GTX-Ti-M2D1GD5/OC
- 120gb ocz agility 3
- 2tb 5400 rpm
- Corsair CX600
- DVD+RW
- Windows 7 64 bit