Wow our children are so similar mine also has a high pain threshold. Once he Burned his hand on the oven, not a peep! He just flinched and walked away! This rules out spankings too ( I know everyone has their opinions and some don't agree with it but that's how I was raised and I think it works, just not for him) Your the first parent who's child was also a "dumper" and my son can sit tearing apart a magazine for hours. We buy them just so he can "play" with them. Our DVD case was another favorite he would throw every single one off (he wouldn't do anything with them, just throw em and go do something elSe) the minute we put them up there he was throwing them off again. Same with toys he had a box of smaller toys (cars, rattles, blocks,etc) that he would dump out and leave until we put them up. Most parents have children that are sorters and have to have things in a specific place.Topic- my son was very much the same way. Everyone called him the 'happy go lucky' boy. He never cried except mainly when it became night time. He over reacted to sounds around him yet under reacted when he should have (peek a boo). The ceiling fan was his best friend. He was a pressure seeker right off the bat. The only thing he did developmentally early was cut his teeth, and even then he got his top teeth first when most babies get the bottom first. Once he got those teeth, he became a biter of anything that wasn't food. He wrecked his top and lower teeth due to biting hard objects, broke them right off. High threshld for pain, too. He never cried when he was hurt. My son has verbal stims, and for him it was the letter P. He could say puppy and baby. His main form of communication was a growl, and by the type of growl you knew if he was mad, sad or happy. It wasn't until he started really talking, he started asking about memories he had but he had a hard time describing things due to language issues. I found he memorized things by colors, and his earliest memory was prior to being a year old. So even for a non verbal child, don't under estimate what they may understand. They very well may understand a lot, but lack the ability to make you aware of it due to autism. My son only heard the last of a sentence spoken to him. My advise is speak in very short sentences, add a word as the child's sentences become longer. My son was a toy dumper and paper shredder. Any magazine or video case that had eyes on it, he tore up. My son still has a hard time showing his emotions, he's the type who holds it in all day and let's it out once he's home. My son out grew many of his younger behaviors, and as he get's older he acquired other behaviors but the verbal stims and repeating he may never loose! I had learned my son needed stims, I couldn't always say no. So at home, he's allowed to a point to have his behaviors, but at school I have expectations for him to find some control. He is a rule follower so school is easier for him, and predictable. Social settings and at home never is predictable.
May I ask what interventions you have thought about or are trying?
As for interventions when he was about 18 months we did early intervention - speech and physical therapy, focusing more on PT because he wasn't walking and I felt he needed that more than speech at the time because, for the most part we knew what he was asking for/wanted. Now he is too old for that program so we are doing ST at a different place and OT as well, even though he still needs PT but its difficult with work and other appointments so I decided OT will benefit him more at this point. I have also considered behavioral therapy but where I live it would be a good drive for sessions, and I've noticed that with his other therapies his behavior has improved.
It was also recommended that he be given a medication evaluation but I'm still iffy on that. We will do the eval and decide from there.