I agree with Debbie that it may be time for you to explore PT. While you may never regain full range of motion, it can certainly help with loosening up those muscles. I had surgery back in June 2002 and I'm currently doing PT as my myofacial muscle was in a constant, tight spasm that made me very limited in motion to the right, as well as causing major problems between the shoulderblades.
Once you find what areas need to be kneaded into submission, massage and heat are helpful. In addition to the stretches you are doing, you might add a monthly massage to the list of maintenance expenses for your body. There are a lot worse things to spend money on