Hi Atlas,
I agree with Susan about trying the Nature Domain Turkey and Sweet Potato. In my experience with food issues over the past few years, your boy is sensitive to something in the Instinct kibble, whether it was too much protein, fat, fiber or grains, but not the chicken. My other girl (not my allergy girl) had soft poos as a puppy like you are describing until I put her on grain free. I have noticed even on grain free she needs a lower fiber food (4% or under) or she starts going more frequently and it gets softer. We also have to stay away from chickpeas–green peas are fine.
Your comment about the diarrhea coinciding with the Revolution is an important point-trust your instinct. Even though it is a topical, it still gets absorbed into the bloodstream (and the gut). You may want to try using just a plain heartworm preventative like Heartguard without any additives for worms and parasites. If possible, try a plain flea product, like Advantage, without anything for ticks. (I found that I only need to use it every other month to control fleas during the warm months.) This all depends on your environment what you can limit, but I would look at options other than Revolution until you get your boy’s gut healed. The ingredients in Revolution could be part of the cause of the sensitivities, or a side effect since the gut is not healthy.
