Reducing milk protein did not really have any effect on me. With reducement of gluten I made good experiences, when it comes to my digestion, but had no effect about austistic treats of me.
So actually I do eat gluten reduced, but not gluten free. Its specially wheat that I avoid, because of it having the biggest amount of gluten in it. So I eat less bread in general, and the bread I buy is rye-bread, which has far lesser amount of gluten (and similar).
But I know from german Aspergerforum, that some people really made good experiences with that (but you need to keep to that diet at least 6-8 weeks, to know if it has any effect on you).
Specially if you have a toddler, that seemed to behave "normal" until you started feeding him with regular food, I´d give that diet a try.