Feel as though you "leave" the clubhead at the top during startdown. Use your right shoulder to move your right forearm and clubshaft downplane towards the ball. Left arm muscular effort is going to create tension, which isn't good in this case at all.
How are you feeling extensor action? That is, through PP1 or PP3? What does it feel like to you? If you're drag loading correctly, the startdown should load the lag and the left wrist should want to remain cocked into the downstroke.