Our son struggled a lot between 2.5 - 4 yo. And when we moved him up into a class that was a better fit intellectually it was a disaster socially, so we moved him back down. I'm not sure there was a "right" fit, but we all survived and he is a well adjusted, happy 6 year old now.
Every kid is different, but I think this age can be hard in general for gifted kids.
My (very personal, subjective) take away from the experience is that a play based preschool with very little "school" type work is often the best fit. Sure he was reading books at home and learning letters at school, but most of the time was actually free play, painting, etc, so it wasn't a big deal. The social and emotional development at that age was really the most important part.
I would also echo that the tantrums, etc for DS are usually a sign of something that needs addressed. If you've tried to make it work with the school for a while and you don't know of any other outside issues at home, etc. it does seem like time to reconsider the school choice.
Is the environment too stimulating? At that age my son became stressed in very noisy, very stimulating environments.
Good luck. It's so stressful, but you'll figure it out.
