Hi Steve,
I finished treatments 2 years ago (chemo/rads), no surgery. I have experienced continued issues with neck stiffness and swallowing. The ENT said that the rads tend to stiffen various structures in the neck.
Then, out of nowhere, my right shoulder and upper arm began experiencing incredible pain (such as quickly reaching forward). The radiation oncologist ordered XRAY and MRI and sent me to an orthopedic doc who says that there is a bony growth and that the bursa is compromised. He expects physical therapy to resolve, else he will inject cortisone. Everyone says that this is unrelated to the cancer and treatments (of course, there are the inevitable age related issues - I'm 64).
Though my primary reason for writing is to help alleviate concerns about your shoulder problem being related to the cancer and treatments, the reality is that you should get an MRI and see an orthopedic doc, preferably one that won't jump immediately to surgery.
Harry