How do you know if you’re over-rotating the shoulders during the backswing? The eyes have it.
If your left (lead) shoulder passes under your chin and pulls it to the right, you’re probably turning too far. (Either that, or you merely need to lift your head slightly at address.) This will not only cost you power and efficiency, it will literally take your eye off the ball and wreck your chances of making solid contact.
There’s an easy way to tell if this problem afflicts you. Just set up to hit the driver and close your left eye. If you lose sight of the ball on the backswing, your head is turning too far, thus blocking the path from your right eye to the ball.
Again, the first thing to do is make sure your chin is sufficiently off your chest at address to allow the left shoulder to move under without taking the chin along.
If your head is properly positioned, practice hitting shots with the left eye closed, halting the backswing before you lose sight of the ball.