Minecraft Lag since Update?

Ever since updating to 1.6.6, I cannot play on any multiplayer servers due to extreme lag. It has a very long delay, and eventually crashes with an error. I've updated my drivers, reinstalled it twice, no mods or texture packs and I am wondering how to fix this. I'm in a minority, as everyone else on the server is fine. Also, when I try to set up my own server on 1.6.6 that map doesnt load and its constant falling. Somebody connected to the server from my router on a diff account and it was fine for them, so I really dont know what to do.