What torrent client are you using and which tracker are you d/loading from?
By the sounds of it all the 100% seeds have gone and so you've only been able to d/load to the percentage of what the rest of the swarm have.
If it's a private tracker, or at least one with a forum, you could request a re-seed on the file.
As said above you need to set your max upload rate to a preset figure as having it set on max/automatic will kill your d/load speeds. The recommend figure is 90% of your max upload speed. So if your on 512K DSL it will more then likely be 256K up. So 256/8=32-10%=28.8 so set it around the 25-28K mark and you should be fine, obviously some ISPs have different rates for up.
2.5Gb shouldn't take you 3 days to d/load though unless your on 128K or dial-up. I'm guessing you haven't been leaving your PC on 24 hours whilst trying to d/load this file? If it's a tracker from the states most of the yanks will probably be coming online and seeding whilst your PC is turned off and your tucked up in bed.
Worst case would be that the torrent has been killed and your left with 87% of nothing lol. You maybe lucky though and able to find the exact same torrent, especially if its a scene release, on another tracker and then you will just have to d/load the torrent file from the new tracker and carry on from 87% where you left off.
Sy