Finally life is normal(ish)
My IBD boy is finally under control from a raw pork diet ( because his sister is allergic to chicken) , minimal if any dry food which causes vomiting- only freeze dried chicken hearts in tiny amounts during nail cutting and brushing.
After many vet visits and testing, I finally did for my cats, what I've done for myself over the years - changed to a species appropriate diet. It wasn't easy or cheap. The cats weren't thrilled with the new food. But taking out the canned food and kibble, they eventually got hungry and now the raw pork is just normal and they love it. I started with novel protein canned food (rabbit was the most effective) and it would help for a week or two and go right back to diarrhea.
The diarrhea came under control slowly but wasn't 100% so I kept researching. Finally I realized it was helped with added raw bone (chicken necks), so eventually I added a small amount of eggshell powder to the pork which firmed the stool.
The morning vomiting - he would find scattered cat litter and vomit if he got too hungry, was the last thing to tackle and it wasn't always easy to tell if he had eaten enough at night to hold him till morning, or would I be up early enough. I bought a wet food refrigerated feeder and I freeze a 3 a.m. meal so it stays fresh in the feeder before it opens. Petlibro is the brand. I can always tell he's too hungry if he starts rooting around the floor for scattered cat litter or eating dust bunnies. I bought the feeder so we could be away during the day and it took me awhile to realize he needed it every night as well.
This has taken a few years to completely stabilize because I had to experiment to actually find things that made a difference. The enzymes and prednisone never gave results and he hated them.
I hope this is helpful to someone who needs it.