I'll probably ride it without the rear brake for a few days and test it out, since it's already off and everything.

I just finished putting on the chain only to find that the cone bearings are loose in my front wheel. At, least I think that's the problem. Unfortunately, I don't have proper tools to fix this so hopefully the guys at the LBS will do it at a discount considering I've spent a few hours and about $100 there on tools and parts in the last few days.