Giant Breed kibble/feeding suggestions needed

I'm hoping some of you seasoned giant breed owners can help me resolve some digestive difficulties with our Great Dane. He is 8 months old, 98 lbs. He currently eats Eagle Pack Giant Breed puppy formula(Dry) and we've been struggling with 'pudding' style poop for quite a while. We've been into the vet more times than I can count attempting to get a handle on why the loose stool and move in a more solid direction. We've changed food slowly to other varieties including Solid Gold, Canidae and our Vet's food. He's been checked and re-checked for worms (by vet) and appears to have no other health issues. While it's not terrible, it doesn't seem normal for this to last so long. I've asked about a raw diet and it potentially resolving this issue and my Vet isn't a fan of raw diet. Any feeding suggestions or solutions would be most welcome.

Kris