Sounds like we might be in the same boat. Have you tried calling VM and talking to them about it yet?
My post on a similar topic.
Give me a bell if you manage to resolve it, will ya?
Since you're using a router, you might want to try connecting your computer directly to the modem and see if that helps your speeds any.
Also a solid piece of advice seems to be to try downloading a large file from
here. See if you get your usual speeds; might help to pin the problem down some.