My heart goes out to anyone who has this kind of problem, since our last GSD was amazing, but he hated people!
I have worked with animals for most of my adult life, and studied wolf behaviour in captivity for a year. This was my pre cursor to becoming a dog behaviourist. I also worked with Roger Mugford which included court work.
I had always taken great pride in training my dogs (including a school environment for socialisation), from an early age, and Zak was no different.
Yes, he should know his place in your pack (bottom). Yes diet is important, etc. etc. so I had no excuse
He ran amok in his puppy class, but passed on time, did well in the middle class and went on to graduate with flying colours to achieve his advance certificate, but he NEVER warmed to people. Despite my best efforts and those whom I had worked with.
He had never had a bad experienced with a stranger, and there was nothing in his background that could have triggered his aversion, so it remained a complete mystery.
I would strongly suggest that you speak to your vet, outlining his problems. He will then refer you to their chosen behaviourist and if you are insured, you will only have the access to pay.
I really hope that mine and Zak's story will help. He was put to sleep last year just before Christmas, and even found the strength to bark at the vet despite the dreadful pain he was enduring. As you can see from my avatar, he was a wonderful dog and the light in my life.