I developed insulin resistance as a T1D. None of my doctors recognized it. I was slowly gaining weight (25 pounds over 5 years) and my insulin just didn't work as well as it used to. My A1c climbed from mid 6% to 8.5%. Some insulin corrections didn't move my BG at all.
I broke its back by going low carb, walking every day, and losing 25 pounds. My A1c dropped, I used 1/2 my usual total daily dose of insulin, and my weight loss took little direct effort. My A1c ranged from 5.9%-6.4% during the last two years.
I've never taken Metformin but I'd be curious to see if it worked for me. Insulin resistance is wicked. I could never predict my BGs and I spent way too much time high. But then the insulin would finally gain traction and drove me dangerously low. Not a nice way to live!
Dr. Bernstein's law of small number is one of the smartest things I've learned. Low carbs = smaller insulin doses = smaller mistakes. It works.
Good luck, I know how tough it is.