Hi Terri
Deb asked if I would pop over from the Lantus Tight Regulation forum to help. I think the ladies have done a pretty good job of explaining those high preshots.
I will see if I can add anything to help clarify further.
Lantus is a long duration insulin which, as others have said, builds a depot subcutaneously. When you start giving insulin shots, you typically don't see an immediate change to the BG because those shots first go towards filling this depot. Once the depot is full, then the insulin you give is used by the cat and you start to see some change in BG. This is the reason we hold the initial doses for so long regardless if you use the TR protocol or the SLGS Approach. The beauty of these long duration insulins is their cumulative nature where one shot builds upon the previous.
When making dose changes, we do it slowly and incrementally. Think of changing course in a cruise ship. The captain can turn the wheel but it takes patience and time for the ship to actually change course. That's how these insulins work...so we all learn patience like we've never known
In TR, the normal range we strive for is 50-120 which is the normal BG for a non diabetic cat. I think when we all start giving insulin, we think it is simple...that you give the calculated starting dose and then the kitty comes into normal numbers and everyone is happy.
That rarely happens. When Midnight was diagnosed, her body had become used to the high numbers as the new normal. When she started getting lower numbers (and they don't have to be really low) or if her BG dropped quickly, then the liver releases counterregulatory hormones and glucagon to bring numbers back up to what the body perceives as normal. We call this a bounce and it can take the body up to 72 hours (six cycles) to clear these hormones and glucagon from the system.
it is important to ignore these bounce numbers when dosing.. If it only takes 1u to get her to normal numbers but you give 1.25u because of the high preshot, then she is going to come down even lower and then bounce even higher. Plus, she would be at risk for a clinical hypo.
Almost all cats on insulin bounce at some point....some get over it quickly, others bounce a long time. But you hold the dose, ignore the bouncy preshots, and dose on the nadir. There may be days when you can't see the nadir for the bounce. That's where you don those patience pants and let the bounce clear before you change the dose.
On cats who are well regulated, like mine, the bounces can be in the 130-200 range. She occasionally sneaks up a little higher but I wait to see what her nadir is before I make dose changes.
As far as what Midnights dose should be now, the 1u was a good starting dose for her; however it wasn't held long enough even for TR. and then it was increased to 2u. So the possibility exists that you've already bypassed her good dose.
Because she only had two shots at 2u before she went to 66 and you shot a reduced dose one cycle in between, I have to wonder if it might be best to take her back to 1u. And I'm not generally one who backs doses down

if you can continue getting a PS test, a mid cycle test, and a before bed test, then you might want to try 1.25u but give it time.
One of the best pieces of advice I've gotten over the last few years is to decide where you want her nadir and then dose for that number. If one dose leaves the nadir too high, take it up a bit. If it leaves the nadir too low, take it down. But lantus likes consistency in dose and time so as close as you can get to shooting every 12 hours, the better. And do not be tempted to raise the dose based on the PS unless her nadir IS her PS which is not unheard of with lantus but it is also not common. The AMPS is usually the last number to come down.
Questions? It's a steep learning curve but you have some really great ladies here willing to help.