Browser lag

The title of this probably has nothing to do with the actual problem, but whatever.

I can’t stand it when my browser lags. The best way i can explain what i mean by “lags” is that the entire thing stops after you’ve requested it to go to a URL. It freezes, you can’t minimize it, it doesn’t respond when you click buttons or roll over them, and it certainly doesn’t load the site you want it to. This happens for about 5 seconds or so, unlags, and then lags again. It does this quite a few times before it even displays the page.

The only thing i can think of that might be causing this behavior is my upload. I’m almost always seeding something on a torrent, and it takes up the full 50kbs upload i get. If i pause my torrent, or if i’m ONLY downloading, not uploading, i don’t have this problem. It seems like the browser sends out a request to the internet, but can’t get out of my connection because my torrent is taking up all the bandwidth. Then it just locks up, and exhibits the “lag” behavior until it manages to squeeze past my upload.

So basically what i want to know is:
A) Am i right? Is this caused by my upload blocking other requests?
B) What do i do to fix this? I tried Opera, Firefox, and IE, they all have the same issue. Is there some setting i need to change to prevent this from happening?

I sure hope this made sense, its kind of hard to exactly explain what is going on :\