Check for busted ports on your modem? Harsh damage to the ports can cause a ton of nuisances. My current modem is busted, we're getting a new one soon, but I sometimes have days where I go 999 very often. The ethernet thing actually is taped down to the modem just to keep the end held up so it works.
For about two months at the beginning of '07, I went 999 like 1-3 times every time I went on Tremulous, and it was always for like 10 to 60 minutes. I could talk still so it wasn't like lagging out a few times a day, which I would have preferred over stupid shit like what I had.