I dunno ... what did your pro do to your swing to make it flatter - tell you to stand further away from the ball? If you ground the club correctly, the length of the shaft and the angle of the shaft in relation to the clubhead determine how far you stand from the ball, assuming you have had your clubs measured to fit you.

How much flatter do you swing now is? It might not even be your swing plane that is causing your new ailments. I can't speak for others but I know when I've had hooking or slicing trouble, I discovered that it was because of my alignment or ball position (further forward/back in the stance) that was causing the problems.

Although golf isn't a high energy sport like football or basketball etc ... it is possibly the most technical sport around. This means that elements of your swing may change without you realising it so it really necessary to practice continually and consult your pro regularly. The secret of golf is to identify your errors at an early stage and remedy them as soon as possible. This is very difficult to do and I know that I have, in the past and probably in the future too, been guilty of trying to remedy problem that doesn't actually exist.