Oh you poor thing. Your DS sounds a lot like my DS11 who is HG, ADHD and dysgraphic. I remember SO vividly a 6 month stretch back when he was about 4 when he absolutely refused to wash his hands for dinner. I had a little step stool, liquid soap and me stationed right beside him for dinner hadnwashing. I would say "Time to wash hands for dinner." and this horrible news produced a huge meltdown every day. For months. He also had trouble with transitions, bath time, teeth brushing, arrgh, arrgh.
It does get better but so slowly that you don't really notice until one day you think "Hey, what happened to the hand-washing tantrums?" I remember four as the pinnacle of difficulty-toddler type tantrums with preschool staying power.
Hang in there. It will get better but your son will likely always lag behind. A neuropsych eval is a great idea. Keep a close eye on the social side of school where your son will struggle. I have found that the crystal ball question that tells about how school is going socially is "who did you play with at recess?"
