Tantrums & aggression in highly sensitive 4 year old

It's possible this is some form of Sensory Processing Disorder, or another sensory-related consideration. If I was in your situation, I would speak to his pediatrician and and ask for a referral to an occupational therapist (OT). 

we have struggled for years with tantrums with our highly sensitive daughter. we had similar issues, hours long, so much screaming and sometimes aggression or destruction. she is now 11 and with her age and size the tantruming was getting scarier and more worrisome. we had a therapist suggest getting a giant trampoline for her. anger is energy and has to be discharged. she said having her jump for some time each day had been shown to help children with big feelings, tantrums, aggression. we were at our wits end and decided to go for it. our daughter has actually been asking for one for years (when i told the therapist that she said often kids will tell us exactly what they need--ha). we've had it since feb and she's maybe had 2 tantrums since then. and they were much less scary than where she was before (she was more like 2-3 tantrums a week). often highly sensitive kids are highly stressed kids, so it's also important to look for areas in life to reduce stress. are they overscheduled? do they have adequate downtime to choose what they want to do? are there ways you can help them make transitions to and from places more easily? we also started looking into more sensory inputs for her (even tho she doesn't present as needed major sensory help transitions have always been such a struggle). so many kids have some sensory sensitivities and there are tools to help them get those needs met. we got her a music player because music is so regulating for her--she can listen whenever she wants or during a transition. also regular snacks are super important for blood sugar stability (it's all about protein). and finally, sometimes littles need big body play with their grownups. check out hand in hand parenting for ways to help them relieve stress and connect with you. these are all my tips. but really that giant trampoline was  a game changer/life saver. i wish we got one years ago. good luck! 

We had a great experience with Rebecah Freeling at Wits End Parenting (https://witsendparenting.com/). She deals specifically with strong-willed children, and gave us a lot of practical advice to deal with our four year old's refusal to cooperate, screaming, biting, etc. We were also feeling like he was taking over all our time together as a family. With some concrete tools, we were able to get to a place where he's much more cooperative and we're able to relax and have fun with him. I was really impressed by how much she enjoyed kids and could put herself in their shoes while giving us tools to be able to function together as a family. Anyway, recommend! Hope you can find help for your little one.

I can't speak to having used specific parenting coach/therapist/assessments, but I learn a lot from the Janet Lansbury podcast "Unruffled". The real turning point for me was when I realize that a lot of times, my children wanted me to physically comfort them while they were upset. Maybe this is what Janet calls 'empathizing', but I didn't really know how that translated until I started reaching out to my kids (as they were crying and screaming) if they wanted a hug and to sit with me. It's hard to not get angry when my toddler starts doing things that I see as 'unacceptable', such as throwing things dangerously or hitting me during a tantrum. But now I try something different first and will ask if they want a hug. It's almost always a yes, and then we try to think of another alternative that would be acceptable to me as a parent and make them happy. If they want TV and I say no to that, I will think of something else they like, play hide and seek, bake cookies, etc. I also try to head off potential tantrums by giving them a heads up in the morning of what to expect for that day. For instance, I don't like them watching TV everyday, so I may say in the morning - today is a no-TV day, so we have to find something else to do (they have preschool, so they have lots of time to not even think about TV, but nevertheless, I still announce in the mornings what the evening plan is when they get home). You didn't mention anything about screen time, but I have noticed that the more screen time children get, the crankier they are when they aren't on screen time - to the point where their behaviors become really unmanageable. Good luck to you. I had a pretty unpleasant 4yo for a year, and things got a lot better when he turned 5.