Your son reminds me a lot of my high-spirited 5 year old daughter. Very intense and your son sounds very persistent too. Things are getting so much easier in our home and more peaceful since we have implemented a new approach. As a parent educator and coach, I was so thrown by my daughter's tantrums and really felt that I had the right tools but couldn't figure out why it wasn't effective.
Now, I actually teach this method with my clients!
There are 2 great resources: The Family Virtues Guide and Transforming the Difficult Child: The Nurtured Heart Approach.
The jist is, you and your husband identify 4-5 boundaries (these are virtues like Respect, Peacefulness, Orderliness, and Obedience). Each of these boundaries has ground rules that are explained during a weekly family meeting to your son: These are examples of our boundaries...
"In our home we have 4 Boundaries; we RESPECT each other by talking calmly without yelling; we are PEACEFUL by sharing and cooperating with everyone; we are ORDERLY by putting away our things and helping take care of our home; we are OBEDIENT by listening to our parents and doing what they have requested."
Each of these boundaries and their ground rules has a consequence.
Example of a ground rule for Respect:
If you are not respectful to family members, then you will spend time in your room to calm down, come out when you're ready to sincerely apologize and you will practice being respectful. Etc. Each one would have a teachable consequence. This is the challenge for parents and so, I encourage you to think about it with your husband.
The boundaries and the rules and the consequence are posted on the wall or the fridge or where ever everyone can see it. I am amazed that establishing the boundaries and the ground rules in an "official meeting" each week has really changed things. I can say, "Isabel, I need your respect right now" and she knows what I'm saying and follows through. It isn't fool-proof but it has significantly improved things.
The weekly family meeting is very fun and positive and the kids love it. We have a special dessert, play a game together, highlight what each person has done well that week, light a candle and talk about a virtue for the week for all of us to practice and review our boundaries.
Also, throughout the day we mention the virtues in her that we see her practicing well and we make sure we emphasize them more than we put our energy and emphasis into the consequences of her misbehavior. Before, misbehavior was always really harped on and a big deal - my response would be immediate and just as intense as her misbehavior. Now, she gets a lot of attention for doing things well "Isabel, I really appreciate how courteous you were with the neighbor" "Writing a letter to your friend is very considerate." "Sharing with your brother right now is cooperative. That makes our home a peaceful place." "You're showing a lot of self-discipline by only taking one cookie. Wow! Great job!" Etc. And when she misbehaves, I'm really unemotional and robotic about the consequence. It isn't very exciting.
Where do you get these words? It's called Speaking the Language of the Virtues. It sounds weird at first, but it works beautifully.
There's more information about these approaches, but I can't write it all here. This could get you started or peak your interest to learn more about it.
If you want more support with it, let me know! Best of luck!!