Lag when joining and exiting server + Slower walkspeed after leaving FL servers.

[Mist]

The first problem you have is to clean your computer. As Barkles said simply de-frag your computer and check if for virus! Its your own computer that is slow and nothing more than that.

Your second problem may be caused by the gamemode, yes. To fix this simply go to options and change the key where you walk slower/faster.

And the addons is not causing this.

If you got any more questions feel free to PM me.