If you experience slow downloads, it could be for many reasons. This can happen for the following reasons:
The person who you are downloading from is using a bandwidth limiter. There are two types: client based and third-party program.
Your Internet connection is shared with others on your LAN and they are using up all the available bandwidth.
Your ISP may be limiting your P2P traffic via some method of packet shaping. Call up the ISP and inquire if they do anything with P2P traffic. You can try to connect to ADC hubs and test your downloads there. As ADC is a newer and more efficient DC protocol it can be still unknown to your ISP's throttling system. If the ISP does throttle you
You haven't set up your third party firewall or internet monitor software correctly
You need to optimize your operating system for your current connection speed
Your Internet connection is DSL, cable, or satellite one with an asymmetrical connection speed,
Your computer is infected with malicious software which altered the low level network settings of your operating system