If I may offer my advice, as I too am still developing my free swing. Now I haven't a clue what you used to bowl like but you look like you have been getting most of the free swing stuff down. The first and second things to a successful free swing aren't even on the approach. So I have to ask, is your fit right? Do you have to grab or squeeze the ball at any point and time in your approach? And second, you look like you pause and take a breath before you go, but do you relax your swing arm and have the weight of the ball distributed in the left? You won't believe how big a difference those two things will make.
Next, I have three drills that I can suggest to you. One requires a friend, fellow bowler, teammate whatever. Regardless, I want you to get in your stance with your arm fully exstended and have whoever's with you hold the ball and completely support the weight. They'll let go and you just let the ball swing once and they'll catch it when it comes back up. The point is for you to feel what it's like to swing completely free. Now obviously things like knee bend and body tilt and how they will effect your swing can't be measured here, but drill number 2 are one-step drills. They are hard and annoying at first because all you get is a slide. However, it's a good way to start developing your muscle memory. And lastly, this is for that huge step out to the last. Most likely you step out there because that is where you wanna line up with to roll the ball. So why not line up out there and walk straight. Your release is pretty strong and you have a pretty good finish so you should be alright. I suggest taking a towel and folding it long-ways so that it is as narrow as a board on the lane, place it just beyond the foul line, find a spot where you'd like to start and walk straight at the towel.
Lastly, have you considered trying a five step approach. I think you may benefit a little bit from getting the ball into the swing or at least started a little earlier. It may be a little weird at first but it may help and not make you feel as rushed. That will eliminate some muscle use as well.
The Demolition Man
Be like water making its way through cracks. Don't be assertive, but adjust to the object, and you shall find a way around or through it. If nothing within you stays rigid, outward things will disclose themselves.