How do I perfectly sync my contacts with gmail?
The best way is to stop syncing contacts via iTunes and do it all over the air:


On your Mac: go to Contacts.app (or Address Book.app if you're not on ML) > Preferences. Under Accounts tab, tick the checkbox "Synchronize with Google" and add your gmail info.
On your iPhone: setup a Google Exchange account in Settings > Mail, Contacts, Calendards. Google has a good guide for that.


After that all your contacts are synced over the air and iTunes will stop syncing those when you attach your iPhone.