I also have a 3.5 yo that sounds very much like yours. He is very intense and has strong reactions to his feelings, usually anger.
I think that our case, our sons intensity is magnified because of his intelligence. Like most 3yo, he has a hard time accepting things that he cannot control, but unlike most 3yo he carries that aggravation with him for hours and sometimes days.
I think it hard to be stuck in the body of a 3yo when your brain tells you that you are no different than your older siblings.
If you find out the magic secret to helping them through this phase, please share it!