You're still on top of the ball. You have your wrist in a strong (looking) position at the top of the swing, but it doesn't appear to be strong in reality. It looks floppy, and collapses as the ball comes down to your slide foot. Then, you hit up on the follow through... however the ball is long gone by then. You've got the technique of the free, easy swing down... but the wrist needs to be in a strong position at the ankle in order to get your hand in it.
Here's something to try if you really want to get the feel of the strong wrist position. Take a lighter ball off the rack, one that fits your fingers, and try to throw a few with no thumb. You'll want to tone it down, meaning smaller steps, and much lower backswing etc... it feels extremely weird to do at first. But, I guarantee that you will get the feeling of the release that you're looking for. With no thumb, you will need to carry the ball in your palm til it's past your foot, or it's going to make a very loud, embarrassing noise! Once you're (fairly) comfortable that, just do the same thing with your ball, and your thumb in. It will be easier if you keep it small a few times before you ramp up to your regular speed. If you revert, go back and no thumb it with a light ball again until you can repeat the motion with your ball. You can do it. I await the video showing massive revs!!