I would give him a copper bolus, and a selenium and vitamin E supplement (selenium and vitamin E is most commonly found as a BoSe shot, or gel)
Multimin 90 is a good supplement shot as well, it covers a lot of minerals.
I would start giving him a high protein grain and work him up to about 2lbs of it a day. 16-18% protein is good. Have a fecal done to make sure he isn't still battling with a load of cocci, and worms. If he is, treat accordingly.
Does he seem healthy otherwise? Good appetite, everything functioning normally, no runny nose, etc?