I know many of you have heard of the first-person shooter for linux, assaultcube. Now I'm not much of a gamer, so sorry if this sounds, well, noobish. When I first installed it via pacman, it ran so smooth that you wouldn't believe it. Now, after a restart, it is so laggy the game isn't playable. I have my video driver installed (xf86-video-intel) and compiz and all of the desktop effects works fine, I literally have only done one thing since I installed assault cube, and that is install Slim (simple login manager) and replace it in the list of daemons (taking away gdm). I highly highly highly doubt it is because of that. I just don't understand what went wrong when I booted up this time.

Generally SLiM isn't run as a daemon. Follow this Arch wiki page to configure it through inittab. Also, have you looked into where all of your resources are going with top?

I figured out that it will work flawlessly when I use gdm to log in, but slim doesn't work for some reason.

And the ArchWiki says:
So I added it to the list of daemons And I generally have like 1.5 GB of memory free, so it's not that