Could you please clarify what you were using before:

1. Were you using an older version of Limewire and, if so, which version?

2. How many Ultrapeers are you connecting to? (You need to enable the View menu-option for the "Connections" screen.)

3. Which version of Java do you have installed? The latest is 1.4.1 and it's supposed to be much faster than the 1.3.x series.

4. Finally, are you monitoring your modem's line-speed (aka connect speed0? I don't mean the "link-speed" which is the communication rate between your computer and the modem (and is always 57,600 or 112k). If the modem is using a generic driver, it will report the link-speed rather than line-speed. For instance, if the "Connect" speed is consistently "57,600" then you're not seeing the actual speed. In reality, you'll never see anything above 52,000 and it should vary.
____________________

All that said, it's still possible that you've found a new problem in the code. Do you have "Act as Ultrapeer" disabled? That would really screw things up if your modem was trying to act as an Ultrapeer.