Gmod 1 core ?? Wtf

Unfortunately, no, the gmod supports only 1 core and no more

There are several addons on the Garry's Mod workshop that allow you to do multi-core rendering. Also, if you search mutli-core rendering on Google you can find some lines of code that you can put into console to double your FPS.

No. Try to change your gmod on beta x64-86 build. It uses Chromium, >4gb ram and better sound codec, as i remember.

Or: You can try some commands for Multicore Rendering (support isn't perfect, don't wait 100% CPU load if ur gmod will lag)