dry food really messes up everything with blood sugar. I don't know what Tibbs is eating, but some dry food is in the 50% carb vicinity. It could easily explain his high numbers, including the black ones. In other words, while he is eating any dry food at all, he may need more insulin, not less.
Have you seen
http://www.catinfo.org? There is a section on there about how to transition a dry food addict on to canned low carb food.
We often see the suggestion on the Relaxed forum to reduce the dose in order to reduce bouncing. It works, because of what i mentioned above. But is reducing bouncing the goal, or is getting a cat into remission the goal? Newly diagnosed cats who become tightly regulated asap have an incredibly high percentage chance of going off of insulin - more than 90% in the first month, and decreasing but still very high in the first year. Take a look
here, and go about 5 paragraphs down from the top of the page where there is a downloadable PDF called "Management of Diabetic Cats Using Long-Lasting Insulins." That's the protocol we follow here on TR, and it's the only protocol that's been published in a professional veterinary journal on how to dose diabetic cats. It talks in there about how to get them into remission.
All I can tell you is that if your goal is remission, you want to move quickly to get rid of the dry food, transition to canned low carb, and get Tibbs into normal numbers as soon as possible. As time goes on, damage occurs to the pancreas's beta cells which produce the insulin. Initially, the beta cells will heal and begin producing insulin again, but at some point the damage is too extensive and the cat will most likely remain diabetic for the rest of their lives.
It looks like Tibbs was just diagnosed 6 weeks ago - that's definitely still early enough, if remission is your goal.
If he were mine, I'd make the first priority getting him off of all dry food. I would've kept his dose at 2.0u while doing that. Even 3 crunchies in one day can cause some cats to go to high numbers, so I'd have left the dose alone and monitored him, while the carbs worked out of his system. Then the blood sugar tests would tell you if the dose needed to be reduced. We have kitties on here that have more than 2u doses that don't eat any dry food, it just depends on the cat. The testing is what tells us about the appropriateness of the dose. Since you've reduced the dose, just because Lantus "likes" consistency in dosing, I'd leave it at 1.5u and accelerate my efforts to get rid of the dry food.
Here is the spreadsheet of the kitty I mentioned before,
Scooter. Look at his spreadsheet on 2/18 - notice that he's on 5.5u of insulin. He'd been increased appropriately per the protocol, and had gotten his teeth cleaned. Linda has 13 cats, and although the others ate crunchies, she was pretty certain Scooter wasn't eating any. But lo and behold, on the 18th the household went dry food free, and notice what happened in the days after that. Scooter went OTJ by the 20th.
Here is one where Trey got into the dog food one time:
http://www.felinediabetes.com/FDMB/viewtopic.php?f=9&t=122601&p=1274806#p1274806 and his spreadsheet - look at
7/30 amps and +3. He was mostly running in green numbers and low blues, and the bite of dry dog food got him up to nearly 200.
I'm not trying to twist your arm, but i know that if your hope is to get rid of the insulin, time is of the essence, and there is no way to know all of this is people don't tell you. For some reason, it doesn't get said much, so I try to make sure that people know so they can make an educated choice. Whatever you decide, I'm always happy to take a peek at Tibbs and give you suggestions.
Enjoy the holiday!
