This is an experience very close to my own. I had my right knee replaced in 2006. I also had aggressive scar tissue immediately after my knee replacement. Ultimately, I had to have two post-surgery knee manipulations where they put me back under and broke the scar tissue up by bending my knee manually. Even after those two manipulations I still had issues with scar tissue. It took almost a full year and a half until I ended up breaking the scar tissue loose on my own when I jumped and landed awkwardly. Although it may be frustrating, sticking with your PT is a must.
@leithlane, have you heard of or tried a brace with hand cranks on it that you use to help with straightening and bending your knee? What does your therapist/surgeon say about your scar tissue problems?