First thoughts would be that it's your isp throttling back on your bandwidth. Try d/loading something from this site:
+ MagnetMix.com +: The Source for Good Content
If the same thing happens with them, then it's probably your isp. If it doesn't then it's probably the hosts your d/loading from.
Also try the suggestions in this thread:
http://www.gnutellaforums.com/downlo...ms-search.html