Which BT client are your using (ABC?, BitTornado?)
I recommend using Azureus and make sure to go through the configuration setup and put your correct upload speed in.
Your upload speed should be 80% of your total. So, for example, if I have 128 kbps (or 16 KB/s) upload speed, then 12 KB/s is what it needs to be limited to.
Pretty much ALL default settings in Azureus are fine.