More and more ISPs are throttling BitTorrent traffic to try and keep users from hogging bandwidth. There are probably more ISPs throttling BitTorrent than people realize. If you are using BitTorrent and you're going through an ISP, you should always use VPN to encrypt your traffic. With the traffic encrypted, the ISP has no idea what your traffic is, so they won't throttle your bandwidth usage since they don't want to throttle what they consider to be "legitimate" usage.

There are a bunch of places that offer free VPN service, just Google for "free VPN" (http://www.google.com/search?q=free+VPN). Or try using BolehVPN (http://www.bolehvpn.net/serv_bolehvpn.html). I've been using them for a month, the speed is great and there's not throttling of my BitTorrent traffic.