I really think his teeth issues are probably playing a part in these crazy high numbers. You said he's due for a dental and in the past he's needed work done every year. Diabetic cats often have bad teeth, so if he had bad teeth before he became diabetic, i'm going to think a dental is probably needed. I would get that scheduled asap.
I think he needs a dose increase as well. I'd go back to 0.5u and see if that helps. The trouble, as you know is that we don't have that much information to be certain those highs aren't bouncing numbers, but it looks like the control was lost and the green numbers gone with the reduction to 0.1u. But when a cat gets into the 30's on 0.25u, 0.1u is the next step, so . . . .
It's common to have to go up and down in dose.
My concern is that you've got evidence that he can go from HI at preshot to 40's 4 hours later (i'm looking at 3/27).
If he were mine, I'd do the increase, but I'd make sure there was food available for him while I was at work and I'd make every effort to try to get more day tests in whenever possible. Do you have a timed feeder yet?
I'd also be testing for ketones twice a day while I was still seeing these high numbers.
When do you leave for the weekend?