Hi Ashlyn @ashlyn901, I can mostly understand where you are at, and can relate to your insulin sensitivity.
It is well known that YOUR body needs the amount of insulin it needs - that is, each of us has her/his own body and only a few of us perform just as “The Book” says we should. My own history over the past seven decades will show that at times, MY body needed 100+ units per day, and currently my daily total, while eating 200+++ carbs a day is about 22 units.
I agree with what @Joe, a guy who has helped me learn much about diabetes, said when comparing Lantus and Tresiba. I’ve used Lantus but not Tresiba, but in my research a while back, I may have “discovered” reasons why significantly few units may be needed.
Insulin sensitivity: Your 90 mg/dl per unit is close to my Correction Factor [ISF]. Keep in mind, that your ISF can vary during different periods of the day. From 5:30 AM until about noontime, I use an ISF of 70:1, the rest of the day, my ISF is 85:1 - not much different than your 90:1. My thought for you is to accept what insulin your body needs, and the rate at which YOU need insulin and don’t let Test Book Averages scare you away; and, eat more carbohydrates - they will help you live a long, and healthy life. Don’t over eat, but eat healthy.