Cable Modem with 13kb Upload?

I have a customer with a Cox Internet cable service, all speed test show fine, but when they connect to a p2p or any other type of protocal to upload they only get 13kb, where all speed test show around 50kb upload. I tried hooking up to another computer and get the same 13kb upload. Both are running Win Xp but with differant settings, I think it must be with the ISP but they say all they can do is a speed test and a tracert and everything checks out ok, but try to upload pictures or an non copywrited material via ftp or other programs you only get 13kb upload. Any help would be great, I have heard ISPs are blocking ports to keep down p2p swapping, but this type of speed is nonsence. Thanks