Is it Prednisolone? A d you have been tapering it down? I know you went to every other day, but did you also cut the milligrams you were giving?
Prednisolone doesn’t stay in the system very long. You should see the full effect of stopping it almost immediately. Within a day or two you certainly will see what his BG is going to be like without it. Now, if he does have actual intestinal inflammation that was being controlled by the Prednisolone and it starts to get worse, that could raise BG. Every case of IBD in my cats has been so different, with some having easy to control IBD and others not able to be controlled well at all. Some were in a lot of pain and others not. Some had severe diarrhea and others never did. Some had vomiting as a symptom and others did not.