Was the physio a Cert. MDT? They must have this certification. I was a general physio for many years and learning McKenzie assessment of the body is completely different. I would not have been able to clearly identify cervical component without learning MDT.
I still put money on your neck John. Again hard to definitively say without seeing you in person. So if you happen to be in Philadelphia let me know.
If they were and found nothing with your neck then it starts to run into other possibilities such as neural tension, thoracic outlet syndrome, etc.