uTorrent speed zero'd since reinstalled OS.

[Unkn0wn]

So i have a 25 mb/s fast download and 2.5 mb/s upload speed on my UPC Ireland ISP, which on speedtest.net goes up to 31.8 mb/s down and 3.2 up. So about 2 weeks ago, since i have this internet, i could download with 3.7 mb/s in utorrent.. that was the max... it technically crippled my internet speed in browsers but at least it did the job.. if i stopped the upload or limited it, it killed the download, but im not a leecher anyway. so then i had to reinstall my OS, Windows XP - Blade Edition SP2 (thats what i always had, and it works perfectly, so the 1st person to tell me tp change to win 7 will get killed! ) . let me make a note that i do remember a couple years back change some settings in utorrent, that boosted my speed, but i cannot find or remember what i changed. so i reinstalled the pc, and now that 3.7 mb/s dropped to 600 kb/s on a good day... and i have tried several setting changes.. could somebody please try and help me out with this? im pretty decent with computers, im learning programming, although net connections isnt my strong point, but i can work with what i have, so please help. thanks in advance.

edit:

I have tried several setting changes, with all of them just making it even worse... i have found ONE so far that raised it to 600kb/s from the 20-30 kb/s from what it originally was..

also forgot to say the port is open, and the 1 im currently using is 45682.

p.s. the general download (like browser download and video loads etc.) are still perfect, just the way they were before re-install (although youtube is sometimes messing around with its buffers, but thats a different subject)