Are your knees flexing? They seem a lil stiff.
You seem to be dragging your back leg (left leg) after you complete the X step
When I look at it a couple times, I keep thinking "are your hips stiffening up" ?
The left shoulder/arm is hanging in the back.. You need to get it involved and complete the core rotation
Hips, chest, left shoulder and left elbow - get them involved and swing away with both sides..
What i see is you using all your power on the right hand/elbow/shoulder and the rest of your body is just responding to the torque/force generated by half of your body.
Otherwise, form looks really solid from beginning to end. A lot of people could watch this and learn how to throw 300.
Here's to many more trees