Please help! iPhone 6 Plus will not sync to PC, sync button greyed out.

After upgrading to 8.3 I am unable to sync my iPhone 6 Plus with iTunes on my PC. When the phone is connected by cable the PC recognizes the phone and it is visible in iTunes, but the sync button is greyed out and the storage bar only shows about 20gb used, all yellow and marked as "other" data even though my iPhone actually has about 90gb of apps/music/photos on it. I am using the stock Apple sync cable, latest iOS update and iTunes. So far I have tried:

-Power cycling both phone and PC.

-Completely uninstalling iTunes and all associated programs in the order recommended by Apple, then re-installing.

-Unchecking everything to be synced (music, photos, etc) then clicking apply. iTunes does send some kind of brief sync with the phone after I click apply but I'm still left with the greyed out button and yellow storage bar. Nothing is deleted from the phone. Re-checked everything same result.

-Wiped and restored iPhone from iCloud backup, still no sync button and yellow storage bar.

I noticed when I check for music "on device" it only shows about 30 songs from a couple of different albums, all with the dotted circle indicating they were not transferred. I actually have a lot more on the iPhone. I've tried everything I can think of to clear these out and nothing works.

Any ideas?