I already had a high-capacity generic ($6 including shipping on Amazon!) on order. So, I thought I would just try replacing the battery first. It's been a couple weeks now, and everything is great. With the new high capacity battery, it's like I have a brand new phone. This is awesome.
FYI, this may be old news for some of you, but Sprint refused to even look at my phone, since I had rooted it. I think that is pretty crappy of them. I realize they can't be responsible for my modifications, but they '''REFUSED TO EVEN LOOK AT IT'''. In fact, my problem was completely unrelated, and they never would have had to do anything related to software. They are either looking for excuses to not work on phones, or looking to punish people who root. If I buy a Cadillac, and then put in an aftermarket stereo, GM still honors their powertrain warranty. We as customers are getting totally screwed. I encourage everyone to complain loudly about these fascist policies.
I also applaud ifixit.com for their info and products.