You need to use a client with encryption, like Bittornado 3.18 or Azureus. I would steer clear of the new version of uTorrent (1.7) though. Certain trackers have banned it because it reports all your BT activity to the RIAA and MPAA automatically. Make sure encryption is enabled if you use Azureus. Encryption fights certain ISPs (incl. Comcast) attempts to limit bittorrent activity. They use bit-shaping (I think that is what it is called) to prevent you from uploading after completing. I used to have the same problem with not being able to upload after completing, but now that I use encryption, I have no problem.