You are going to take the thing out anyway, I'd say try changine brushes first, they are only a couple of bucks and a few minutes with the soldering iron. If you do go with a new alt, just remember that if you go with an aftermarket one, you will need to be real good at taking the alternator out and puting it back in. Thats because you will change it alot. Look at the above post, dude's on number 13!! One time deal with a toyota alternator and you don't have to worry about changing the alternator 13 times.
Also keep in mind, if you are the type that likes mudding, mud can get inside the alt and push the brushes off the slip rings, and the alt won't work. So keep it clean. I watched my brother go through four pepboys alternators before he sprung for the toyota one and hasn't had a problem since. On the other hand, he got real good at changing his alt.
