My iPhone 6 Plus disconnects during sync!

I have this massive problem that I totally ignored up until now...

I have never been able to sync my iPhone to my MacBook Pro!

Every time I try, the sync starts and then ends after maybe 15 seconds. And then I get that same annoying message that tells me that "The sync could not be completed because the iPhone was disconnected!"

I've tried everything... New cables, taking things off the sync... like music, podcasts etc. I've even tried syncing via wifi, but it's always the same result!

Now I tried to shut down all the background programs, like "Little Snitch" and other apps. But no luck!

I have the latest iTunes and my mac is a MacBook Pro (Retina, 15-inch, Early 2013), 2,7 GHz Intel Core i7, 16 GB 1600 MHz DDR3. And the latest OS X with all the updated it want me to have!

Any ideas?

And please... PLEASE... Don't tell me that I should try to reinstall the whole computer and do a hard reset on my iPhone...

I don't think I have it in me!

Or is this all some elaborate scheme from Apple, so we all have to upgrade our iCloud space and sync it there?

Seriously... Please help!

Thanks!

/Marcus