OP, I just read your previous posts about your puppy. Hopefully the new food is the answer, but if the diarrhea comes back I would suggest you have the vet check for giardia again. Often it is very hard to catch....it definitely should be a very fresh stool sample.
If it is a food intolerance, my guess (and I am not a professional, just sharing my experience) is that another regular food may cause the same issues. He very well could have IBD. I have a pup that used to have intermittent diarrhea and funky stools....we put him on Hill's Ultra Z/D and he is fine now. Another pup with a diagnosed case of IBD is on home cooked food. She had a scope done, so I know exactly what she has. There are a lot of tests that can be done with these pups....I would suggest that if the diarrhea comes back, you discuss with your vet the GI panel that is sent to Texas A&M.
Hopefully, the food has fixed it, but in my experience, I have never had one food affect a pup in such a way. (not suggesting it was not the food...just sharing my personal experience.
)
Good luck!