It sounds to me like this is an illustration of the very first lesson of NSA.
Why do you hit the ball right? Not because you come over the top, cast, stay back on your right, etc., but because your clubface is open (and all those other things are effect, not cause, of your clubface being open).
So, you can use the towel plane board and be relatively on plane but still slice because your clubface is open.
I'd say go back to NSA and work on grip, twistaway, and 'maintaining the twist', as from what you've told us here, it doesn't sound like you've fixed the clubface.