A couple requests for your spreadsheet. In between the day you stopped Vetsulin and you started Lantus, could you add a blank line and label it "start Lantus". It's too hard to see over in the Remarks and is an important milestone we need to see at a glance. Also add a couple more lines after the last shot in 2025 so it easily pops out that you are now in 2026. Normally people have a different sheetsheet tab for each year.
As for what you should do next, let's start with food. If you can stick with low carb wet food (FF pate I think?) then that's great. But you need to spread meals out more in the AM and PM. Instead of once lump of food with each shot, think in terms of less food at preshot and some mini meals thoughout the day and night. A meal every couple hours to mid cycle is one way to start. You want some recent food to be available when the insulin is starting to work or onset, which is typically 2-3 hours after the shot with Lantus. That food will help keep his numbers more steady. Ideally he'd also have some food available around nadir (low point in the cycle) if his numbers are quite low then.
OK, next about Lantus dosing. We have two dosing methods. Take a read through the Dosing Methods Sticky Note and see if you'd like to follow one or the other. It depends on your goals for the cat and lifestyle that suits your situation - that is, as long as he's only getting low carb wet or raw food. With both the dosing methods, we determine how to change the dose baed on answering this question "how low does this dose take my cat?". Or, what sort of nadirs are you seeing. The low point in a Lantus cycle is typically 6 hours after the shot, but can vary a lot by cat to cat, or even between cycles in the same cat. One thing this also means, we don't vary the insulin dose based on preshot values. This dose mean you'll have to try to get a few more blood glucose tests in between the preshot values. You do want to be able to answer the question "how low can this dose take my cat" before you increase. Preshot values don't answer that question.
I suspect 5 units is too much insulin. Looks like you shot 6 units tonight. Please try to get a test before going to bed tonight to keep him safe. Maybe go back to 4.5 units tomorrow, and this time try to get some data mid cycle to try to get an idea how low he's going on that dose.
Are you home testing for ketones? With a reduced insulin dose, it's always good to make sure ketones aren't creeping in.
Tips to catch and test a urine sample Ketones present are something to worry about. Anything above trace means a visit to the vet.
Next, take a read of the Sticky Note on the Depot. Lantus is a depot style insulin, meaning it takes several days for the depot to build and for you to see what a dose is really capable of. WIth our dosing methods, we find consistent dosing is best. Any time you skip a shot or shoot a reduced dose, you restart the clock on how many days you have to hold the dose.
how often are u feeding? only twice/day? does he get snacks? also, try to be as consistent w dosing as possible. increases are .25 u at a time; .5 u if higher than say 3-400 i believe like its been for u guys, will tag moderators tho for the right advice on dosing.. and you only increase after 6-10 cycles. get u a caliper, if you dont have one. that helps immensely and is the most accurate (syringe markings can be egregiously wrong) 
(and for future, taking him off might’ve been a bit premature.. but i cant say.) also the site has great info for everything. here: 
