I know I'm not a LW dev, but I'd just like to chime in with my 2 cents here if I may.

To me, it sounds like something upstream might be affecting your ability to upload... like at your ISP. Is it possible that they might be filtering traffic to and from your system? The reason I ask is that you stated that you removed your router from the picture and the problem is still occurring.

One thing you could try is just to download and install another Gnutella client like Gnucleus or something just to see if the same thing happens within it. No, I'm not saying you should switch to Gnucleus... just use it as a testing tool for now. If the same thing happens within Gnucleus then it's probably safe to say that it's probably not a problem with LimeWire and it becomes a greater possibility that something external to your Gnutella client that's the cause.... if you're not having any other problems with your internet connection, then it's also probably safe to assume that your internet settings aren't at fault... which then leads us to your ISP as one of the only other fault points. If uploads in Gnucleus work, then it's possible that something in LimeWire is at fault (in which case, I'm at a loss).

Sorry, I can't be of much more help than that... like I said, I just thought I'd chime in my 2 cents.