Why do my downloads become really fast, then really slow, etc...?
Any my uploads, which I cap at 11kb/s, are practically flat?
See screenshot to explain:
PeerGuardian2 is an IP blocker program especially designed for P2P software users.
It uses blocklists for the blocking, but IP ranges can also be configured manually. Pre-cofigured for blocking are RIAA, MPAA and many others.
PeerGuardian is installed seperately from Azureus.
SafePeer is a plugin for Azureus that performs the same function, although I am not certain if it uses the same blocklist.
SafePeer is installed through Plugins/Installation Wizard in Azureus. For full instructions see here
Also available in Azureus 3.0.2.0, is Tools/Options/IP Filters, which allows use of the PeerGuardian blocklists directly in Azureus.
I use SafePeer only, so I do not know the entry to put in, but I am sure it can be found.
Both the SafePeer and the IP Filter in Azureus also block those who send bad data regularly.
As far as your NAT, if you have not already, you should take the Tools/NAT Firewall test.