Try mat_queue_mode 2 or -1, disable multi core rendering and enable it again to see if it fixes the issue. And since you downloaded that .cfg that broke your game go into the launch options of your Garry's Mod and type "-autoconfig", start once, exit, remove command line and set-up your video settings like you had before. Make sure you removed that .cfg I mentioned earlier so it doesn't fuck up your settings again.