Drew,

I can see that you are a big guy and you have some good mechanics. I really like your glove side along with how well you get your arm externally rotated with your chest leading your body after front foot strike. I wouldn't change a thing with you except for your major issue which is very poor separation. I know that when your are on a mound and you are throwing live you have a lot more separation in your back shoulder to back hip than your video here but it is an issue as you can see in these few frames. Your hip and shoulder are in sync.

How to fix this?

It all starts with your back leg. When your front foot lands your back leg should be triple extended and foot flipped over. I hate to use Joel Zumaya as an example because he does one thing perfectly and another thing horribly. What he does wrong is his arm is abducted above and behind his head. This is why he tore off his shoulder bone this season but I want you to notice his back leg. It is extended and flipped over. It is flipped over because after the drive or triple extension of the back leg the hips are now open and the back foot is dragging. This is creating optimal hip to shoulder separation or core torque. I believe to generate this much torque you must learn to triple extend your back leg before front foot strike. This is what you are not doing. This is because you are not driving off your back leg. You are falling off of the mound.

I am putting together some great videos on how to train triple extension and separation. In the meantime, everytime you throw the ball do not let your shoulders fire until you hear the drag of your back foot after triple extension. This way you have a stimulus response to tell you when you have achieved hip to shoulder separation. I hope this works. If not I will have videos hopefully soon!