I'm sorry to hear about the tantrums. Our gifted DS7 had his share of tantrums prior to becoming a homeschooler. It seems that after we started homeschooling, we were able to "hug" and rationalize our way out most problems.
However, he wasn't the worst tantrum thrower in the family! Our worst was our DS6, who became our son at 15 months. From the day he entered our house, he threw tantrums that would last 5 hours or more. (Sadly, this is not an exaggeration.) He exhibited all the behaviors you listed, plus a few more! To solve this problem, we used more tough love. I can happily report that we rarely see these tantrums anymore.
With child #1, lots of love, encouragement and common sense seemed to work. With child #2, lots of jumping jacks, laps around the yard, deep breathing, and leg/back massage seemed to work. Neither were easy on us as parents. #1 was emotionally draining because we absorbed the pain, and #2 was emotionally draining because we had to appear aloof and seek inner resolve to make it through the consequence.
I hope you can find the right thing for your son. I can't imagine that you could go wrong, because it's obvious you care deeply!
