Concerned granny

My grandson is six and in first grade. Child needed to be held almost continually since birth just to sleep for 20 minutes. Still does not sleep through the night. Has never had regular bowl movements. Will go for days. He does not like loud sounds, constantly has hands in mouth, make animal noises incessantly when trying to talk to him, hardly eats for days and then can't eat enough. This is very disruptive in school.

He does not have any friends, pinching and hitting others and himself at school and during play dates. He prefers to play alone but at home insists Mom spend every minute with him. Preoccupied with one thing for weeks, dinosaurs, then transformers, then star wars, etc. Watches TV constantly but likes the same thing over and over and screams if anyone talks or gets in his viewing way during his shows. Very abusive to his mom. Hitting, pinching, biting, etc and seems to enjoy it. Wants very active, almost violent playtime and will not quit or take it down a notch when told. Timeouts and taking things away doesn't faze him. He makes animal noises and hits self during time out. Screams orders to everyone. "Bring me this", "I don't want to do that" and then flies into a rage that can last for a long time if is told no.

Doesn't want to play board games, but loves to be read to. Loves video games but has very low tolerance for not getting everything right ie, winning. Parents took to pediatric neurologist and psychologist for evaluation of autism, learning disability, anything to explain behavior. They were told everything okay and child needed discipline and boundaries. They are frustrated and household is in an uproar most of the time. One thing I find particularly frustrating is he constantly says "I love you" and gives hugs and then turns 180 degrees and hits or throws something. Child is extremely bright(high IQ)and masters any task very easily.

School is boring to him but school won't advance him to next grade level or challenge him because his social skills are so immature. What to do to help them? We have all suggested psychiatric evaluation but I also think the SPD checklist is very valuable diagnostic tool we can use to partner with medical evaluation. Maybe change diet to gluten and diary free? Any ideas?