Hi Jason-
He does in fact need to stay on large breed puppy formula especially because he was neutered too early. This is critical for correct growth. Of the two options you have offered, Diamond Large Breed Puppy is the only option that would be appropriate for him.
Also, before jumping to the conclusion that he is having an adverse food reaction, you need to see the vet to eliminate all other causes such as fleas, mites, environmental and seasonal triggers. Adverse food reactions are not as common as people on the internet would have you believe, especially not in a 4 month old puppy.
