Orally fixated 4 year old

Is there anyone who has an older child who still chews on things like a baby? My 4 year old puts everything everything in his mouth to chew on like a baby would, and he often chews toys completely apart on purpose. Like little cars, he will chew the wheels off. Little people, he will chew the arms off. Any animal, the same, he will chew parts off. He will chew on shoes, socks, utensils, books, clothes, everything. I remind him constantly to get things out of his mouth and bought him some chew safe toys but he’s not into them and he does it so absentmindedly that I can’t seem to break him of the habit. What can I do?

(He is diagnosed ADHD and I have suspicions of autism but his pediatrician seems to disagree)