Slow BitTorrent Speeds

Yesterday I noticed that the total download speeds for my torrents will not go above 10/KB's. I am currently using cable internet provided by Source Cable in Hamilton, Ontario. The reason why my torrents won't go above 10/KB's is a mystery to me because whenever I download legal torrents, something off the newsgroups or standard http it's always blazing fast. Also I am NOT using a router just a standard SB5100 Motorola SURFboard Cable Modem. I have also tried numerous things such as using different ports and patching tcp/ip but both of them didn't do anything. I'm obviously curious as to why this is happening although I do have a couple questions. My first question is could ftping from my PC to XBOX make my torrents go slow? (please note I haven't downloaded while doing this). My second question is how come when I download legal torrents such as open office and slackware they go very fast but then fluxuate? And obviously my third question is does anyone have any ideas how to fix this?