Hello and welcome.
It's hard to say how 3 units is doing with your cat, without seeing some blood sugar data. I do see the blank spreadsheet, so thanks for setting that up. Once you get some test data in there, we'll be able to help you decide if 3 units is too much, or two little. My girl got up to 8.75 units of Lantus, but that was slow and steady increases to get there, testing to make sure I didn't pass a good dose. Since Little Man started this diabetes journey with DKA, I'd be very reluctant to lower the dose until you have enough data to say he's on too much insulin. Cats vary a lot in how much insulin they need.
Is LM taking anything for his asthma? Any other medications? Sometimes necessary medication can cause higher blood sugar, but we just work the insulin dose around it.