Download speed gets slower and slower

Hey guys / girls, I'm having a strange problem when downloading files. The download speed starts at about 10kb/s then gradually over a few seconds it drops and drops until it is at around 50b/s (yes bytes!).

I've spend about 2 days tring to figure out whats up - been through the 'Slow Downloads' FAQ on DC++, my ports are mapped sucessfully on router (using upnp), speedtests are fine (14Mb/s) consistently, firewall (AVG) allows DC++ etc

I can't even get file lists from people as it takes a lifetime! The strange thing is that when I exit and restart DC++ the download speed starts at about 10Kb/s and drops down again. Hmmmm

I am getting so frustrated I want to punch my dog! (lol not that i would ever do that!)

Any help / ideas would be greatly appreciated (by me and my dog!) :-)

Thanks.