I have the same problem. I'm currently reading a book by Dr. Kidwell that has a good chapter on target panic. In it, he describes two types of target panic. One is premature hold, which he claims is common among sight target shooters, and the other is premature release, which he claims is common among instinctive shooters. From what you've described, it sounds like you have my problem, the premature release form of target panic.
Anyway, I haven't gotten to the point in the book that talks about "curing" target panic, if there is such a cure, but it's interesting reading, and what the rest of the folk on here have suggested sounds good enough for me to try as well.
One thing I've noticed about counting while holding is that as I aim, no matter how many times I tell myself to count to 4, 5, 10 (or whatever), I can't seem to do it. But if I don't aim at a specific target, I can draw and hold forever if I want to. What helps me some while aiming at a specific target is when I tell myself that I won't release when I come to anchor, I'll only count to 5 or so and then let the bow back down. Sometimes that happens, and sometimes I give in to the urge to release anyway, even after I told myself not to, but usually (although not always) after I've held for the full 5 or so count. Those shots are usually right on the money, unlike my inconsistent premature release shots.
Anyway, hope you continue to improve and get yours under control soon....