They do seem to swing quite a bit. Have you thought about perhaps switching Kisa over to Levemir? It seems to help kitties who just bounce around on Lantus. It helped stabilize Mikey's numbers significantly.
I got it through DCIN, so I have to use what I have. Though the past 5 days, we were using different needles (the box I bought inexplicably had a single 10 pack of huge needles in with the other 90 normal ones) so his dosage may be off as well