is my cpu bottlenecking my my gpu

Solution
Not really, and don't think if a gpu is a bit more expensive that the cpu that there is a bottleneck. If you dont have a pentium 3 with a gtx 750 it won't make a diffrence more than 1 fps.
The A8 5500 is somewhat weaker than the Pentium G3258, and that GPU is comparatively low end. The should work well together.

I'd lok at turning off some of the effects in the .ini file (like motion blur) to stt if that helps.

C:\Program Files (x86)\Steam\SteamApps\common\Viscera Cleanup Detail Santa's Rampage\UDKGame\Config\UDKSystemSettings.ini