Your symptoms do sound like instability. An MRI is important but standard X-rays with flexion/extension components will give the most diagnostic benefit. Make sure you see an orthopaedic spine surgeon to understand what your pain generator is.
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.