Things that might help:
No TV/ media after dinner
Turn down the lights after dinner, try to create a soft and quiet atmosphere
A hot (as hot as you can safely make it) lavender bath
A massage with some lavender lotion
Warm milk with honey, or a night time tea with honey (chamomile and peach is one I give my boys)
I would also model a nice quiet activity after dinner as well. Maybe some knitting, or reading a book? I would try to avoid being 'busy' at times when you are trying to encourage him to wind down
Someone suggested that perhaps you should try giving him his own space to sleep? I have heard of those few babies/ children that really do sleep better by themselves in their own room or bed. Not suggesting CIO, but maybe it's just too hard for him to unwind when he has you or your DH right there next to him.