Try this:
Go to LW's menu bar, Tools -> Options -> Advanced, Performance tab. Then check to disable both Ultrapeer and TLS abilities. These can both have an effect on system performance.

You may also wish to limit both your up and download speeds to 10-15% below present settings for both regular Gnutella files and torrents: Tools -> Options -> Transfers, Settings button. Check the limit up and download bandwidth options. Example: if present upload or download speed is 100 KB/s, then change to 90 or 85 KB/s. Do this for both.