Welcome to FDMB.
We can try to help but can you answer some questions for us?
1) 6 units is a very high dose of insulin. What was your starting dose and how often were the increases?
2) Are you hometesting?
3) What are you feeding your cat?
4) Are there any other health issues going on with your cat?
My first thought is your cat is not regulated and you are dealing with neuropathy. Also, because of your high dose, you may also be dealing with Somogyi rebound. What this means is that in order to protect itself from becoming hypoglycemic, when too much insulin is given, the body produces extra glucose. So with the extra glucose in the body, your cat's diabetes can not be regulated and this in turn can cause the neuropathy.
If you are not already doing so, you should learn to hometest. Once you begin hometesting, you also should consider lowering your cat's insulin dose and basically start over with increasing it until you find your optimal dose. Insulin should only be increased after you have been on a consistant dose for at least a week to give the body time to adjust to the new dose.
Also, if you are feeding dry food, that could also have affect on the BG levels. However, please do not change your cat's diet until you begin hometesting. If you switch to a low carb diet, without lowering your insulin, your cat could become hypoglycemic and that could be deadly.
Please answer the questions above and also start reading the information on this site about hometesting, diet and hypoglycemia. We will be glad to help the best that we can.