You say that this behavior occurs after he has escalated. One possible explanation is that he scares himself. A sensitive, introspective kid might worry that he has gone too far. He loves you and doesn’t want to lose his connection with you.
Try this: The next time it happens, offer a hug or bring him onto your lap. Reassure him that you love him, too. Tell him that you think his tantrums get pretty scary for you both. Ask him what you can maybe do so he doesn’t get so very angry and upset. Perhaps the two of you can find a way to interrupt the tantrum before it scares both of you. Make sure you have this conversation as calmly and matter-of-factly as you can. This isn’t intended to be a way to scold him. It’s a way for the two of you to put your heads together to solve a problem. Then try out whatever you came up with.
You may have to have this conversation a few times. Sometimes people agree to try something that simply doesn’t work. The task then is to again reassure and go back to the “drawing board.” Calmly say, “Well, I guess that didn’t work. What should we do now?”
Your son is lucky to have concerned and involved parents. Instead of escalating in response to his out of control behavior, you are looking for answers. Hang in there. A little boy who has so many positive attributes can actively help solve the problem if given love and the chance.
I wish you well.