Motherboard controlling my gpu clock speed?

Hey everyone, first of all here are my computer specs:

Windows vista 64 bit
AMD athlon 64 x2 6000+
DDR2 4gb
Gtx 560 2gb
A15g v1.0 motherboard

I just upgraded my graphics card from 9800gt to the Gtx 560. Previously on my 9800gt when I would overclock it, if I increased the GPU clock more than 20 mHz the performance would mysteriously drop significantly. Upon closer looking, I discovered that when I'd increase the clock it seemed that my motherboard acted in what appears to be a safety precaution and would actually cut my GPU clock , memory clock, and shader clock mHz's in half. The only way I could find to remedy this is to reset my GPU's clocks back to default and to reset my computer.

Now that I have my Gtx 560. All seemed OK at first as long as I didn't make any attempts to overclock. But I found that once I hit a scene in any of my games where its demanding on my GPU and my FPS drops below 20, my motherboard seems to do the same mysterious under-clocking as when I overclocked my 9800gt and it cuts all my clocks mHz on my GPU in half, and just like before the clocks refuse to go back to their default amounts until I reset my computer once again.

Well, I'm not even sure if it's actually my motherboard causing this but its just my theory. What do you guys think is going on here? Is there anyway I can over-ride this mysterious under-clocking?