Degrading Performance

I don't really know if this is the correct place to post this or not, so bear with me.

My config: http://www.digitalstormonline.com/comploadsaved.asp?id=689897

I purchased my DS computer back in May for gaming purposes and it was amazing... the first two months. I maxed BF3 at 120 FPS and could play games at that FPS or more even (Minecraft said 4000+).

Now over the past 5 months the performance has degraded significantly. Around July, I began noticing a drop in performance. BF3 dropped to around 90-100 FPS and dipped in gun fights. Killing Floor caused the FPS to fluctuate. RUSE went down to 20 FPS (Keep in mind that the FPS was maxed before this).

Cut to now, BF3 now is around 45-60 FPS, most games I've had to reduce the resolution (and in some cases that does nothing such as Minecraft, Planetside 2, Arma 2, and WarZ). I've also reduced the graphics settings but sometimes that's not enough. Another thing is benchmarks, running 3dmark gets me a score like others with my set up. 3d Vantage just doesn't work (gives me vertical lines). But, other benchmark scores are up to par with others, just bad in game performance.

Of course I've contacted DS support, over the course of 5 months, we've tested the graphics cards, reseated and tested RAM sticks, CPU stress and temperatures, PSU replacement, clean re install of Windows, virus checks, updated BIOS, and re installed drivers. But, nothing has happened, the issues still remains. During the PSU replacement, the person I had installing it said that the motherboard could be the cause, but I don't know.

Finally, consider this post as a last effort to see if anything can be done or ideas on the problem I'm having before I first send it to a local repair shop and, if nothing gets fixed from that, sending it in to DS.

Thank you for reading.