First I will assume that this was an ACDF (anterior fusion) of C5-7.
“Tightness and some irritation in the upper back, trap, shoulder and pec area” generally is an indication of pain generated by the lower cervical spine (C4-T1).
Obliquus Capitis Inferior and/or superior muscles are occiput to C2 muscles and would not cause the lower neck and shoulder pain you complain of. These muscles are more involved in headache and base of skull pain generation.
I would suspect continued pain as you describe as generated by a level not involved in surgery (C4-5 or C7-T1) or from a pseudoarthrosis (lack of fusion) of the levels involved with surgery.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.