I think you should file for the TDIU....If you are leaving your job because of the stress and anxiety or anything else that is related to your service connected MST and/or any other issues that you are rated for, then yes I believe you should apply. However, just a piece of advice....I wouldn't just say you are retiring but that you are leaving your job because of your service connected issues. IU is for Veterans who cannot maintain employment because of service related issues and you should receive it because you can no longer be gainfully employed because of those issues, so you are losing income because of those issues and should therefore be compensated. Its because of those service related issues what retirement pay you get will be lower, your social security will be lower and if you have any kind of employer matched 401k, that will be lower and because of this and other things I don't know you should get compensation.
I have a 70% PTSD rating and I am TDIU. When I was younger I could work and suffer through what was going on in m,y head and Its not easy and you pay a professional price, but most importantly a personal price and there comes a time when you become overwhelmed and you just can't do it anymore.
I got a certified VA rep to help me with my claim. She is very good and knows what she is doing and made my claim less stressful. She would get 20% of any retro pay, but for me not having the stress and anxiety involved with the claim was worth it. I'm not recommending her because I would get a cut...I won't and I don't want it. I am just a vet helping another vet.
If you want her name and number, you could at the very least talk to her and she would advise you if you have a claim that can be won. Just let message me and if you want her name and number I will provide it.
All the best and if you need to talk just let me know.