3.5 yr old hitting issues :(

My 3.5 son hits kids and also teachers. He hits kids when he doesn't get his way and he also hits to get attention/when he wants to initiate communication or play with them. Teachers have said he picks younger girls more often. Some times when we are around we noticed that he is very gentle with babies and kids want to play & share. According to his teachers his hitting is unpredictable. He also touches himself and gets very upset at that time if we/teacher try to stop. We have also heard complains like he doesn't like to sit during circle time. We have checked his attention span. As long he likes something he can spend hrs together. Also, can sit in front of TV for hrs! In general he is a smart kid. He knew all the Alphabets, many rhymes and used to count till 20 by the age of 2. Though he was an early speaker he doesn't talk very fluently yet. (I should add he has picked up lot of English in past 6 months). He had a Nanny who used to speak different language and also went to multi language day cares. English is his second language. Some times I feel he has hard time communicating to teachers & other kids. He does hit me sometimes. Talking to him and Time outs did not work. I have been trying 123 method and taking away toys, which works for a while but then only at home. He is the only kid we have. Only interaction he has outside the house is at school. He is not exposed to domestic violence or any fights. We both work and respect each other. He is quite affectionate, loves his dad a lot and wants him around all the time. He loves to socialize with people. He also does not respond to his name many times though he is listening and does selective listening/response. Some teachers have complained about him not making eye contact with them. According to us he is ok with eye contact. He is obsessed with tractors/trucks and wants to play, make stories and poems around them(quite imaginative actually) and is not too much in to coloring or writing. However like us to read stories to him. We are trying to take him to story telling session so that he will sit better in the circle times. I noticed that he only sits if it interests him or else just doesn’t bother. Even when he is sitting it appears as if he is not paying much attention though he amazes by singing that song later.
He also doesn’t respond to questions the way most of the 3 yr olds do though he is capable of doing. We need to probe him a bit to answer. He still does drool once a while. It took us like 6 months to potty train him. Our main worry is him hitting at school and getting expelled because of that/getting branded as a “bad boy”. We had to change two preschools in the last 6 months due to his hitting kids and not lsitening to teachers problem. I am trying to understand why he does that and how to help him with that. I checked for autism and ADHD symptoms in him from what ever I have read and I did not feel that’s the case.
Any advise/techniques appreciated. Thanks in advance.