Well, it doesn't seem like MORE prednisone is the answer.  After a conversation with the vet, we took his pred back up to 5mg in the AM, and 2.5 in the PM.  Not good.  WAY too much water/pee/food/runny poop.  In addition, he was panting in his crate.  Back down to 2.5mg AM 2.5PM.
After a couple of days at that level, we'll try The Hill again tomorrow early.