Phew so many questions...not sure I understand them all - but I will do my best to answer them.
I have taken a closer look at my problem and it seems to be only this one torrent that behaves that way - I tryed another one and the DL speed was normal on that one. According to ABC the Seeds on "the problem torrent" are 10 and peers 14.
I have not tried another download system - I did in the beginning and had all kinds of problems so i stuck with ABC
I did post a HJT log 2-3 weeks ago regarding another problem I had - and my system was cleaned thoroughly (i think at least...just did what I was told) and I have not installed or downloaded any programs since.
Hope that answers some of your questions - maybe this has something to do with the torrent - not my system?