Base your next move on DM59’s advice - It’s solid, positve and has your well being in mind.
AFTER that, and you get a clean bill of health … incorporate this into your delivery motion:
-your glove arm – ALL OF IT, has to move in concert with your pitching shoulder … well beyond it’s present posture. In other words, when your pitching arm is “just about” at its high point B-4 your start your release consideration(s), that glove arm has to have the chest moving towards it… and just B-4 meeting your chest … it must move with the glove arm’s shoulder --BACK out of the way with that side of body(glove side) so you actually exchange shoulders - glove arm’s shoulder with the pitching arm’s should … or as we say … bury your pitching shoulder into the catcher.
I wouldn’t be a bit surprised if - currently, you feel a slight TUG on the muscles just behind your neck and pitching arm shoulder.(?) The most common reason for this — other things be equal and qualified per the instructions of DM59 above, is the glove arm and glove arm shoulder is not allowing those muscles to MOVE OUT OF THE WAY… thus giving the mass of muscles and bones on your pitching side … NO WHERE to releave all that energy… and space to move to.
Like I said, after following DM59’s advice, try my suggestions in very, very slow time and get use to it. Seventy(70) rep’s a day “in slow time” in front a mirror is good practice to not only feel the relaxation of the shoulder muscles exchanging by also to actually SEE the posture routine that your tying to accomplish. When you start to step-up the delivery speed a bit and … again … you start to feel that TUG … you know your shoulder exchange is retarding itself like your old way. So, take the delivery speed down a notch … regain your composure and shoulder exchange discipline and start over.
I should note that a media of this type has huge restrictions so PLEASE, see a professional like DM59 said first.
Best wishes on your progress.