I'm not a fan of elimination diets. They are a LOT of work and potentially expense too and may or may not work. What happens if they work, when do you reintroduce things or do you keep your child on that diet for life? What happens when they go to a party or a friends house?
I would aim to avoid as many processed foods as possible and high amounts of food colouring, but the diet you have him on already sounds pretty good. You're getting in some fruit & vegies and at 2.5 that's pretty good. I would read books on behaviour management such as 'The Spirited Child' or 'Raising Boys' because it may be you are expecting different behaviour than is 'normal' for his age. 2.5 year olds are pretty full on and challenging at the best of times.
I hope this doesn't offend, but I mostly wanted to let you know there are other options rather than completely changing his diet, which if not done carefully could cause nutritional deficits.