You're asking the right questions Abbey. It's a lot to take in and understand, and you were at a higher dose before the diet change. The diet change made a huge difference in dose for my kitty Max way back when he was first diagnosed, so you may still need some adjusting for Georgie. I agree with the others on trying out a lower dose, keep testing and monitoring, and, depending on how it goes, slowly walking the dose back up, if needed. Hopefully, that'll give Georgie a chance to get used to better numbers and less bouncing, and then you can slowly increase. I know you've already been working it pretty slowly, waiting 3-5 days before increases, but it may be that Georgie's body needs more time.
The following is just an example and not meant that you should do Georgie the same... When my Max relapsed in December and went back on insulin, I started at .5u, even though my vet recommended 1u, just cause I wasn't sure if Max would really need 1u. So far, he hasn't ever made up to 1u yet, so I feel good that I was more conservative than the vet. The vet used the weight formula to calculate the dose, so she wasn't wrong either. It was a gut feeling on my part and because I had been testing Max even before he started on the insulin. Even with starting at .5u, I dropped it down to just a little less (.4u) cause there was a teeny tiny bit of bouncing and I felt I needed to learn better how the insulin was working on Max. Max dropped into the 50's a couple times at first, and, with being so new on the insulin, I wasn't comfortable with that yet. Anyway, we went from .5u, to .4u, back up to .5u, to .6u, to .65u, to .75u, over a 2-3 month period. You don't have to take it as slow as that as it will depend on the BG's that Georgie gives you. Just an example of taking it slow. Every cat is different and even a slight change makes a big difference for Max. You may not see as big a difference on slight changes. This is more an example of patience, and the very kind folks here have needed to remind me more than once to be patient. ;-)