I would change the protein source. If that didn't work, I would try grain free but I'm not a big fan of grain free unless it's for a working dog. Sorry. Maybe I've been around horses too long but I'm sceptical of foods with a 40%+ protein content. Why does the average dog or puppy need so much protein?
Carbohydrates (grains) are a common cause of digestive issues. They break down more slowly and take time to digest. And dogs don't start digestion in the mouth, like we do. Plus their digestive tract is shorter. All this adds together to make for a situation of undigested food in the system, causing gas, large stools and other digestive problems.