Have you tried prone hangs? If your PT will allow it, it's are a great tool to regain full extension. I'm about a month out of my second acl surgery and I had issues with extension the first time so I was really faithful this time and regained full extension pretty quick.
My PT had me do the prone hangs like this:
Roll up a towel, lay face down on my bed with my legs hanging off the edge, just above the kneecap, at the bottom of my quad. Place the towel right there, above the kneecap and just let the weight of your leg pull it down and straighten. At PT he placed a weight on my ankle but I was too afraid to do that at home, it was painful. It didn't take long until I got full extension.
And Linda is right, keep pushing forward. Hope this helps.
Good Luck with recovery.