I am having a similar problem. I just upgraded to LimeWire 3.8.10. For the first few hours I was enjoying 50-70 kb/s like I always have with LW. Not sure what changed, but next time I started LW a few hours later, downloads were at 1-14 kb/s, and this is where I've been stuck ever since.

This is what I tried so far:
1. set my upload bandwith to 10%
2. disallowed partial sharing
3. max upload slot at 1
4. adjusted my firewall in OS X to allow LimeWire/Gnutella
5. force local IP is on
6. set search result speed DSL or higher
7. set search result at quality 3 and 4 stars

I sent an inquiry to my service provider about my ISP, haven't heard back yet. What else can I try?