I have had lots of problems with my red setter from a puppy,
I had a very thin puppy who did not put on weight easily, and all the dried food I gave him went straight though him with the same problems as you have . I tried him on tinned it was good out put, but he was not putting on weight and was still hungry.
I also tried him on pure which is one that you have to re hydrate with warm water, very good but did not help him put on weight.
the only one that worked with copper was raw , out put very good , firm , he also put on some weight and is doing very well on it.
I was not a raw food fan but now am all for it ,
The company I use is Luna and me they do patties and it is very easy to use.
You could also try cold pressed food which breaks down in the tummy quicker and is better than kibble which sits in the tummy for a long time.
Your dog may be like mine and does not do very well with dried food.
I hope that this helps and you can help your dog with a diet that helps his tummy.