A buddy recently pointed out to me that I'm not using my hips at all on my drives. Sure enough, after he taped a few of my drives I noticed that it's mostly my upper body making the throw happen and my hips are just along for the ride. I don't know how I break 400 with that form.
Anyway I just recently went back to step one, took out a bunch of putters and began practicing standing drives with my hips leading and the rest of my body following. It helped a lot and feels very good on the pull through.
I noticed that your form is somewhat similar to mine with your hips following your upper body. That's one thing I would work on if you feel like working on something. Most people don't complain when they throw over 400.
By the way, this works wonders on approach shots too. I'm usually pretty decent with approaches, but when you're standing still, rotate your hips back then forward while your body is still facing off to the side, the hips begin to pull your body into the rotation and everything comes out much more clean.