Hi Susan,
Great job getting the spreadsheet going.
Are you able to keep monitoring closely over the next few days? If yes, you could try progressing the transition to low carb only - especially as Timmy seems to be getting less interested in the dry by the sound of things.
You could leave out some wet food for grazing (but make sure your tortie doesn't nick all of it!

). By testing regularly you'll be able to see how the food change is affecting BG levels and reduce dose if necessary.
Once the food change is safely completed and Timmy has a few days to settle you could then work on refining insulin dose.
Mogs
.