In LW go tools > options > advanced > firewall config. Change LW's listening port to something in the range of 49152 - 65535 (eg 65000) > apply > ok.
You can try any ports in that range.

Your ISP say that they don't throttle p2p & I can't find anything to suggest that they do. Have you tried using LW outside of peak hours?

You could also try the advice here (the first few posts by murasame), if you haven't already.
A few things to consider while configuring Limewire for optimal performance...

Posts merged onto existing thread.