As I understand it, the "going up slowly after doing a curve" part of the method is there to prevent "shooting past" a dose. Looking at your SS, I'd personally want to get some more +2 or +1 in (I know you can't normally, but if you're around I'd try and grab those) because if you were giving too high a dose (I'm not certain you are, TBH) then you might be seeing a drop then, early in the cycle, causing him to bounce right up for the end of the cycle. Your curve before upping to 3.75 doesn't have anything before +4, so in theory there could maybe have been a drop there?
This is the extra info I'd be wanting to see to be really sure you didn't shoot past the dose. But it's also quite possible his insulin needs have changed. Would you be able to do a curve today or tomorrow (not sure where you are in your day) with more tests in it at the beginning of the cycle, to make sure there's no risk of missing anything? (If you're still at home, that is.)
Not sure if this is helpful or not but it's all I can think of right now.