GG-
If your dog has gas on one type of food and not the other, I'd go back to the old brand. Also look at the quality of stools. A healthy dog should not be farty and should have solid stools.
"I was told this is a good brand"
Good brands for who?

Point is, not all brands are good for all dogs. One should look at the ingredient list and then see how a dog does on the food.
http://dogaware.com/
This is an excellent site on dog feeding info. It will help you make decisions for YOUR dog.
Please note re puppy foods, esp large breed puppy foods!! Note the ratio of protein and fat! High protein is OK but should be balanced with appropriate fat, not low fat, high protein. Most manufacturers reduce fat to reduce caloriees to slow growth -- that is not the point! Unfortunately manufacturer's "dumb down" to pander to owners who erroneously feed too much in general. (People somehow tend to like roly poly puppies.) Feed high quality food, balanced correctly (ADULT FOOD) but feed less if puppy is getting fat (thereby growing too fat, thereby putting too much stress on joints)!
Sorry.... rant over.
Anne