I just wanted to add that I had a similar experience with grain-free kibble with my youngster, too. I tried Evo (which she LOVED), Taste of the Wild (which she didn't like all that much) and Merricks Before Grain (which she loved, but gave her bad gas) she would not gain any weight on these foods, as good as they are. I was convinced that I should not feed anything that had grain in it, but it just wasn't working for my dog.
I know a dog that has been fed Natura's Karma for her entire life (she's about 2.5 or 3 years old) she has always looked like the picture of health! I asked her owner what she feeds and she said her Vet swears by Karma! So I bought some and have been feeding it for a few months. Despite the fact that it is extremely grain heavy and goes against everything that I have been reading about dogs and grain, my dog is doing fabulous on this food! She is gaining weight, has great energy, a coat so shiny you gotta wear shades
and good firm stools. She also really likes it! Which helps...
Here is a link to the website....
http://www.karmaorganicpet.com/