6wks post-op, open shoulder surgery. incision doing well. but, experiencing severe pain radiating down arm to ring/middle fingers. what's going on?

Nerve pain: That's an irritated nerve either from c spine or brachial plexus, possibly even terminal branch. Not likely that it is directly related to shoulder surgery. The C7 branch is not near the shoulder unless a very large or posterior approach made.

Neck issue: You need to have your neck evaluated for possible nerve entrapment in the neck. Not like l;y to be from shoulder unless nerve got injured at the shoulder surgery. Go back to the surgeon for a reevaluation.