Probably shaft length. Try choking down a bit on the driver and even taking a shorter swing with it.
I went through the exact same process you are describing several years ago, and I believe you are ablolutely on the right track. But this should not be confused with ultimately not breaking the wrists. The comments by the gentleman in the post above about wrist break being integral to swinging are accurate, and refreshing to read. You'll get back to that I am confident. In order to clarify my point, consider the idea, employed by many, of "holding back wrist release".
What happens to muscle tension when one attempts to delay release? The muscles in the hands and forearms are then "keyed" in the wrong direction! Why do that? What you are actually doing by attempting to NOT break the wrists, is keying the muscles in the direction of the hit. And that is exactly what you want. Eventually you will discover how to manage muscle tension in such a way as to, rather than prevent break, RESIST break, allowing club C force to eventually take over and break the wrists with the muscles then keyed in the direction of the hit, allowing for a natural release as you term it, and a very powerful strike.
I actually choked down on all my sticks when at the point you are. When I learned to employ the above, I was dead flaberghasted at launch rate. A lifelong 140 8 iron suddenly became 160 choked down with a "3/4 swing". Dead straight. This is why I inquired as to the definition of full swing. If that definition does not include the individual's viable range of motion (IVROM), then it is an inaccurate and misleading definition.
As far as your hand/torso position? Please sir, don't let anyone talk you out of that. If you assign to the arms/hands thier proper function, which is to maintain positions and tensions established at address, (And that is quite enough work for them to do), you will soon be swinging in the manner the gentleman is refering to; freely but properly keyed, with BOTH arms maintaining position (they are both holding the club, aren't they?), and I expect the right elbow will be less bother.
The reason I asked about connection is because all of the above is contingent upon it. If you don't maintain shoulder leverage, it's kind of hard to make any of the above work.

Joe Hill