Limewire actually does not encourage the queue to be filled to its maximum capacity. It stops sending back search results as soon it knows it will not be able to immediately service an upload.

Most of the time uploads get in the queue because of alternate locations, Unless your ip address was listed as an alternate location for some file(s) on a lot of hosts, hardly anybody will enter your queue once your upload slots fill up.

However, the issue with the very slow uploads not getting killed is something interesting. Can you see if it happens only to gtkg's?