Hi cdroge,
In my experience there are two very typical hang-ups on the turning lock. One has to do with *over* rotation, which doesn't seem to be your problem the way you described it. The second is much more likely -- a lack of proper usage of the 2nd step (the lock itself) -- so I'll address that one.
Many students tend to race through the 2nd to the 3rd step, without enough attention to the usage of the [man's left, lady's right] foot to create the necessary action. There are two surefire signs that you have this problem: (1) If you can execute a reasonably comfortable open impetus, but not a turning lock to PP, and (2) if you or your partner doesn't have the ability to stop entirely on the second step.
Obviously in momentum-based dancing, one should not expect to be able to stop completely at any given moment. However, if you have a particular area where the dancing runs away from you, it's sometimes a good idea to counteract it by learning to stop, to give yourself the opportunity to analyze and correct the action, before injecting momentum back into it.
So try stopping with your feet crossed, and if you can't, that's your first lesson. Once you can, then take step 3 very slowly, paying particular attention to the use of your left (lady's right) foot as you leave it. Make sure, like an open impetus or pivot to promenade position, that you're using good principles of inside/outside of turn, and that you're not turning the lady to promenade until after she has shifted her weight entirely onto the 3rd step.
Hope this helps.
Regards,
Jonathan