iPod touch 64GB not synching playlists (again)

I have a 64gb iPod Touch, iOS 8.4.1, iTunes 12.3.3.17, on Windows 8.1. The trouble I'm having, and have been having since I got the ipod almost 2 years ago, is that it periodically stops synching with my computer; and what I mean by that is nothing will update, the songs I've added won't go to the ipod, and my playlists won't update. The only solution I've found so far is to do a complete restore on the ipod which, with 7,000 songs takes about 3 hours. Then it will work ok for a while, until it doesn't. I want to know if there is some other background problem that is causing this as this issue is getting really old. The thing is, I also have an iphone which has synched perfectly every time. Any help you can give me would be much appreciated. Thank you.