[guygee]

It's like Phishblowz says, you can do your best to push the bytes out, but if your peers are not also pulling the bytes then nothing much happens.

Actually I have noticed these kinds of big fluctuations when one or more of your peers are firewalled. It is hard to maintain a constant connection with a firewalled peer, so the upload pulses up while you are connected then goes down to zero when you lose a connection. Same is true if you are downloading from a single firewalled seeder, the DL often pulses high, then drops to zero cyclically. I am not a big expert on the bit torrent algorithms, but this is just what I have noticed by watching.