Hi Steph,
Just thinking "out loud" here:
I read Meya14's post to you on another thread about maybe trying Lantus or, if sticking with ProZinc, giving a consistent dose to Chuck for a bit. She was also discussing your concerns about Chuck's weight. I know he's been driving you nuts lately with spikes and dives and you're trying to address this by responding with doses tailored to those numbers at AM/PMPS. I think Chuck has that ultra-responsiveness to insulin dose that Teasel has. In Teasel's case, I'm keeping my dose changes micro in size and holding them as long as I see some positive effect even if some numbers are wacky. I know he can't tolerate frequent or large changes - they'd make him bounce into high numbers and get stuck up on the ceiling. He becomes insulin resistant quite easily. That's what happened before his DKA at the end of March this year.
Chuck needs to gain weight, as you've said. I don't know the details of your feeding regimen other than your comments about him starving all the time - consistent with high BGs. Meya14 has said elsewhere that some cats need higher carb food to support larger insulin doses so that their BG numbers improve and they'll gain weight. Then they can gradually have the doses and feeding changed to reflect an improved FD status.
I'll flag
@Sue and Oliver (GA) and
@Meya14 for their thoughts.