Which model of Linksys are you using? There is one range of their routers that are unreliable when run in UPnP mode. (when using games or p2p I mean)

If you are having these problems when downloading torrents, keep torrent downloads to a minimum. Torrents sometimes use too many connections which flood the system & router. I have experienced something similar with torrents .. but it's not necessarily due to speed but how many connections the torrents have. I do not use LW for torrents however.