Garrys Mod Runing Slow

Gmod is for some reason running extremely bad. It often kinda pauses like it has to load in the game. The loading of a map is über slow.

My specs are:
CPU: I5 3570k 3.4 GHz Overclocked to 4 GHz
GPU: XFX Radeon HD 7970
Ram 8 gb 1600 Mhz
Mainboard: MSI Z77A-GD55
Resolution: 1920x1080
Windows 7 Ultimate 64-bit

(User was banned for this post ("Wrong section" - Gran PC))