you could test this theory asking to a friend of you of running a small server on his machine (at the moment no examples come in my mind) and then you can use my tcpfp tool (
http://aluigi.org/fakep/tcpfp.zip) specifying his IP and PORT so that it will make various sequential tcp connections to your friend.
another hyphotesis can be the router/modem you use which usually are not that good, but I don't know what type of line you have.
for the other question: find the cause and you have chances to fix it. I can't help and don't have other ideas.