How come when I'm on Sharezza, the downloads are consistently low - 4K is huge. But when I'm on Limewire I can watch someone from Sharezza upload from me @ 50K?

Make sure you're only using one network at a time & your problem might just be 3/4 solved.

BTW Shareaza users are reknown as leechers on the Gnutella network because they download from gnutella users such as those who use LimeWire, etc. but use most of their upload bandwidth on the other networks ShareAza can connect to. Stick to one at at time & I'm sure you'll do a lot better. Downlding & Uploading on the same network are often related in their success rate. And of course, one of the mediums Shareaza connects to requires just that.