I have been frustrated with several issues:
1) Smart Playlist not syncing correct (not matching iTunes library)
2) Songs staying on my iPhone and iPad that should be coming off. Songs that should be going on not.
3) iPhone and iPad filled with OTHER (amber) taking up space on the phone/pad.
4) iPhone and iPad continually getting stuck on last Step during syncing.
5) Neither would Restore. Get stuck on last step of download and then give a timed-out error.
Here's what I did and it seems to have worked.
By the way, I have had no problems with my iPod Classic.
To fix:
1) Make sure you sync and back up your iPhone/iPad (even though it's not been fully correct).
2) Make sure you back up to iClould (this is key). If you don't use iCloud, sign up. It's free. Otherwise you will lose all that is saved to your device. I did lose some photos, so email yourself any that you just would cry if you lost).
3) I have my device checked with SYNC THIS DEVICE...OVER WI-FI (although I don't think it has any affect on these steps).
4) Go to SETTINGS>GENERAL>RESET>ERASE ALL CONTENT AND SETTINGS
5) It'll make sure you really want to do this and you will have to enter any password on the device.
6) It takes a few seconds to clear. It'll then reset.
7) Follow instructions on the device (same ones you did when you first got it). During set-up, turn iCloud on with Apple ID. Once you go through the set-up, the device should have some Apps that come free and it should have no content.
8) Connect to your iMac (not sure if this will work with a PC, but should).
9) Set up as new device (I did not want to restore from what I had because I didn't want to put back the same problems).
10) Select the Apps, Music, Podcasts, Photos, etc that you want on your iPhone/iPad. This step takes time because you will have to arrange the apps on the page you want and reselect the items you want on the device.
11) Sync/Apply. This will take some time if you have a lot of items.
12) After the sync is complete. Disconnect from the iMac and go to Settings. You'll want to reset (how you want them) the Notificiation Center, Sounds, Wallpaper, add your email, etc. If your Contacts and Calendar are connected to your email address (Outlook), they will all come back once your email is set back up.
13) There, likely, will be some small adjusments you will want to make (custom ringtones, time to lock-screen, etc) that you will make as you go. These are minor.
14) I did these steps the other day. Played the iPod all day today (over 100 tracks affecting many Smart Playlist). Came home, synced the iPod (no problems as normal); synced the iPhone and then the iPad and both synced fast and accurate. What a change :-)
Hope this helps! Time will tell.
Coach Dave