My iTunes won't sync all my songs with my iPod

I'm using auto sync, just like I always have, and the box is checked to sync all songs with the iPod. If you check the bar at the bottom of the sync page, it *thinks* all 5000+ songs are on the iPod, and there's plenty of room left. But when you play one of the songs on the iPod, it says playing 1 of 800. Some of my songs are unchecked to not sync, but we're talking 100 max. So how do I get the missing 4,100 songs to copy??

The iPod is an iPod touch with iOS 5.1.1; Mac is using OS 10.9.1; iTunes version 11.1.3.