Speed test show your upload and download speeds by timing a set amount of data. They don't really check your connection. Here speed isn't that big a factor, quality is.
Is your problem only with the game? Do you use other on line games with out any trouble? To you bop around the internet with out a problem? If it is with this game only, it might not be a connection issue.
I'd run ping plotter. Set it up and let it run for 10-15 minutes, make sure you are pinging the game server, not the web server (see Skuzzys "connection" post for the addresses).
If you have Comcast, and they are messing with the priorities like Skuzzy says you won't be able to pin point that, but you should be able to see the quality of your connection. If your loosing a lot of packets, or the delay is real high (over 300ms sucks) you'll know its your connection causing you grief.
On the other hand, if its in the 30ms-40ms range with no packet lose, your connection is fine and you might have to look else where. Next, I'd run a DXdiag and post the first third here. Maybe you added a program or two recently and its running in the background and eating up CPU cycles (hit
and check how many processes are running).
The more info you post, the better we can help.