internet

hi,
i got a problem. i did a speed test on my cable modem and got good results. While surfing the net or downloading files of the net, i can get speeds in excess of 100kbps at times, but on average i atleast manage to get 70kbps, this is the same with morpheus. however, at mIRC, i can't seem to pass 35kbps. The peculiar thing is after 30mintues or so..the speed drops to between 10-15kbps. I know its the mIRC, i have configured it to the max, also I know its not the person i am downloading from because other people on the channel have managed to download speeds in excess of 60kbps from the specific Fserver. anyone know what it might be? i have tweaked my internet settings with tweak xp as well. any help appreciated.