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Innova is one of the best foods on the market, so if I were you, I'd try to stick with it. No to Eukanuba.
Most vets get kickbacks from major dog food dealers -- and on top of that most of them are not canine nutritionists.
On to the weight gaining issue -- how much are you feeding Cubby? Do you free feed and make food available 24/7? If not you might try that. Puppies have small stomachs and many would prefer to eat several small meals or to nibble off and on all day.
Itchy Flaky Skin-- try adding some cold pressed fish oil, or salmon oil to the diet, there are several good commercial brands -- Grizzly Salmon Oil is a good product. I have had good luck with Coat Handlers, be sure to thoroughly rinse all of the shampoo out of his coat before conditioning. I usually rinse with running water for 5 minutes, it may be excessive, but what can I say. There are many good shampoos especially made for dry skin -- you have already gotten some good suggestions, and will probably get more.