Hi Angela,
Glad to meet you

Don't forget to give Jimmy some delicious treats for being a good boy before and after testing. You can use deli meat, rotisserie chicken (no skin), freeze dried meats, Kitty Kaviar (bonito fish flakes), or even cheese. That might help him sit still for DH.
The DM if canned, is not very good quality food, believe it or not. You'd do a lot better with Fancy Feast or Sophisticat even. Personally I use Friskies, but there are tons of good OTC canned foods. Here's the ingredient list on DM:
Liver, poultry by-products, meat by-products, water sufficient for processing, chicken, salmon, oat fiber, salmon meal, guar gum, potassium chloride, carrageenan, salt, Vitamin E supplement, calcium phosphate, taurine, thiamine mononitrate, zinc sulfate, ferrous sulfate, niacin, calcium pantothenate, copper sulfate, Vitamin A supplement, manganese sulfate, menadione sodium bisulfite complex (source of Vitamin K activity), pyridoxine hydrochloride, riboflavin supplement, Vitamin B-12 supplement, biotin, folic acid, Vitamin D-3 supplement, potassium iodide.
Pretty crappy huh. Organ meat should not be the #1 ingredient, and there is no actual muscle meat listed before the 5th ingredient, which means there's very little in the can. Also of concern is the oat fiber. You can tell muscle meat because it just says the species, ie: turkey, chicken, salmon. That's the good stuff for kitties, lots of protein.
Onto your dosing.. I see you've been very cautious and consistent with your increases and that's good. I see your dose reduction test on the 3rd and 4th. Glad to see you didn't hold your dose low there. These numbers are not indicative of rebound, you just haven't gotten to your dose yet. In the early stages of treating diabetes, it can often look like a lower dose did better. That's because initially, the body fights back a little bit against the insulin. Just keep on going til you see some really good numbers, he does need more. I would recommend your next dose increase be soon. I am going to get a friend of mine, Nancy and Cody, and ask her to help you with the dosing. She's very familiar with Prozinc.
You're doing a great job with all this testing, I'm very proud of you! Your vet sounds pretty good too, though I would also recommend you see if you can catch him peeing and get a ketone test since his numbers are so high. (((hugs))) and welcome again!