Darn it, it didn't work!
I downgraded to 3.7 again and the posts are still gone. The upgrade must have changed something else. I'll reupgrade to 3.8 since it doesn't work now anyway. Might as well keep the newest version.
I'll wait for instructions. Thanks for your help.
Apparently this is a very common issue after WP updates. I've seen hordes of people having this issue since Wordpress 2, so now I'm surprised it hadn't happened before. FYI, it's not theme related. It's WP related. The way I fixed it (after trying a million different things) was to delete the ht.access file, then go to wordpress settings and reset permalinks to default, then deactivate all plugins. That made the posts and pages come back. After that, I reset the permalinks to what I had them before, reactivated all my plugins, and voila. Back to normal.
Why the error happens or why it gets fixed by resetting those things and reenabling them right after, is still a mystery to me. But it works, and I'll stick with it. Glad I didn't inconvenience anybody around here. Thanks for the awesome theme. I hope this helps other people who may have the same issue.