Passednerve conduction test on left shoulder but i have a large mass of muscle on shoulder/ neck arm goes numb when lifted could be pinced blood vesse?

Thoracic outlet: Your description leads me to suspect that you compress your brachial plexus when you elevate your arm. You could possibly also compress the subclavian artery or vein in addition. See a local vascular or thoracic surgeon and get this assessed. An emg-nct, if done with modern brachial plexus techniques should clarify these issues. Maybe get opinion at washington univ in st louis, mo.