Hi Ggolden2,
I know it's not helpful to hear "the experience is a little different for each person", but it truly is.
I'm hitting 6 months this week, after rotator cuff repair/debridement, and I think I was probably in a similar position as you at 4 months. Range of motion came back very slowly for me. Make sure you're pushing yourself hard enough when you do your exercises. Check with your therapist about how much discomfort you should have if you're pushing yourself appropriately.
It will come. Don't compare one day to the next, as I found it went up and down and could be depressing not to see noticeable improvement, but when I compared month over month, I could see the progress. It can come so slowly, mere degrees at a time.
Even at 6 months, I still have some range of motion to regain...5-10 degrees in each direction. Behind-the-back was the trickiest, of course.
I still have pain. Sleep is rough...a couple of hours at a time, but that's better than when it was a few minutes at a time. It still hurts me whenever I use my shoulder, particularly "above the shoulder" movements, but my therapist tells me that it will all sort itself out over time.
I suppose there's no way the medical professionals could truly prepare us for what this experience is really like, but I find myself wishing that I'd been told more about what the day to day recovery was really like.