There's a lot of confusion on the high 36 plan.
You do not actually retire until you collect retired pay (age 60 in most cases). The retired reserve does not receive retired pay; they are in fact still a control group of the Army Reserve.
It matters not whether you serve in TPU, IMA, IRR, or retired reserve, you will still accrue TIS for pay. So long as your 60th birthday is some time after March 8th 2026, you will cap out for basic pay in one of these statuses.
If you are discharged, it will remain as the average of the highest 36 months prior to discharge. If that happens in March, it will go back to March 2011.
It is possible for retired reserve members to be activated, but you based on the difficulties we have facilitating voluntary transfers, I consider it unlikely unless you have extremely high demand skills.
Over all, it sounds like the retired reserve is what you want.