Hi Erin, thank you for posting your videos, and for providing good context as to where you are and what you’ve been working on. I am a big fan of Alan Jaeger’s long toss program. You might also look at information from Ron Wolforth, Derek Johnson, and Eric Cressey.
In terms of your videos, I have one predominate thought: First Movement. I’ve attached an image that should be illustrative. Your initial movements are all backwards, and reverse-rotating.
For each image in the sequence, you’ll see an orange line that marks the starting position of your head, which is basically straight up from the left front leg of the chair behind you. You don’t get back to that point until almost foot strike.
As others have pointed out, your first movement should be to the plate, and every movement designed to get your release point as close to the batter as possible. Every foot is 3 MPH in the batters’ eye. Look at Greg Maddux.
Moving back and reverse-rotating means that you’ll need to swing back around to get on plane, and that is very difficult to accomplish with any consistency. I see this twisting motion a lot and it typically causes issues later in the delivery (e.g. arching the back and the head flying out to hit the release point.) In addition to twisting, you also have a significant upper half tilt (second image in the sequence) as denoted by the blue line. Your spine is almost at 10 o’clock. This combined with reverse rotation are typically signs a pitcher is getting around a strength or mobility issue, and are compensating by trying to generate other momentum. In my experience, this impacts both velocity and command, and can place undue stress on the arm.
Given all that, once you get the strike foot down, your body seems to reorganized itself pretty well! I think you have a lot of positives to work with and by addressing first movement, you could realize greater success on the hill, not to mention a jump in velocity. Stay positive, keep working, and enjoy pitch you get to throw!