my upload is set to a max of 30kbps, which is much, much slower than the downloads I get.
If you actually wrote what you meant to say, then you may still have it configured wrong. Upload and download speeds have nothing to do with each other, and on most modern broadband connections upload is MUCH slower than download. I, for example, have 6Mbit download and 512kbit up, and I don't actually get either of those numbers.
If you have your UPload speed in your torrent client set to a higher value that the actual upload speed your connection offers, then ALL traffic will stop working properly, up OR down. As Consultant said, if your upload is maxed out, then web browsers and even the torrent client itself have no spare room to ask for more stuff, and if they can't ask, they can't download.
So even if you have, say, 10Mbit down, if you have 256kbit up (which is only 32KB/s theoretical max--remember that there are 8 bits in a Byte), and you have your torrent client set to, say, 35KB/s up, then NOTHING is going to work whenever the torrents are asking for more than about 26KB/s.
Again, I'm going off of what you just wrote, maybe you've got it configured fine and I'm just misunderstanding. If not, though, you want to go to SpeedTest.net when you have nothing at all running and see what it tells you your actual upload and download speeds are. Then take those numbers, multiply them by 0.8 to give some overhead room, and plug those numbers into your torrent client. So if SpeedTest.net says you're getting 4000kbit down and 300kbit up, set your torrent client to 3200kbit down and 240kbit up (which, since Torrent apps almost always measure in KB rather than kbits, will be 400KB/s down and 30KB/s up).
If you've already done this and it's still acting up, then maybe you've got a bum ISP, or possibly a bad router.
Incidentally, if it's JUST torrents that run slowly and everything else is fine, you might make sure you've properly forwarded a port on your router to the computer running BT--you can find instructions on every Torrent client site, and if you don't do that you'll never get a functioning torrent download. Most modern clients will warn you if this isn't set right, though, and if your router supports UPnP your client can automatically configure it for you.
Just fyi you get the best dl/ul speed's by setting your upload max to 50kb/sec. No higher, no lower. Trust me on this.
I assume you meant 50KB/s, not kb (lowercase b is bit, uppercase B is Byte, by general convention), but either way that's going to depend entirely on what ISP you've got. If your upload is only 256kbit, then setting upload to 50KB/s will kill your internet connection entirely. I can say that for a fact with my connection at home, for example--I've seen it do that when I accidentally set it in that range.
If, on the other hand, you live in Japan and have 10Mbit upload (not at all uncommon with a fiber optic connection there or elsewhere in Asia), 50KB/s is ridiculously slow--you could probably be uploading at 600KB/s, and I see peers out of Asia doing that all the time. Same goes if you're on a campus network--here at work we see about 7Mbit up, real world, so if I wanted to get fired I could comfortably seed at 700KB/s if I wanted.
It all depends on the actual, real-world speed of your connection, hence the need for a SpeedTest.net check or similar.