Do you need to go through MEPS to go from the IRR to Reserves?

No, you don't have to go through a MEPS to transfer to a drilling status. You're in a different component and haven't been discharged from the military.

If you're in the IRR, you are accounted for through HRC* directly. Contact your talent manager regarding transferring to a drilling status.

Finally, for a PHA - request one online*

I do have to ask - weren't you given any of this information when you were transferred to the IRR? At a minimum you should have been told who is tracking you now.
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* HRC IRR Division - https://www.hrc.army.mil/content/Individual%20Mobilization%20Augmentee%20and%20Individual%20Ready%20Reserve%20Division
* Requesting a PHA - https://www.hrc.army.mil/content/Periodic%20Health%20Assessment%20(PHA)

Is it possible......... if one wants back into a TPU status from the IRR that a quicker path might be to find a Drilling unit and commander willing to take the IRR soldier and just submit for such transfer.

Poof, done...........?????

I was under the impression the IRR administrative process was more or less just an administrative unit that holds IRR soldiers as a place holder. In that it operates more or less the same as another unit would in terms of moving people into and out of the unit.

If that's the case then all one would need is to submit a DA4651 with the signatures of the gaining commander and the authority of the IRR. Regarding the IRR soldier's medical readiness would merely be the problem of the new unit.

I would think the USAR would jump up and down at pushing soldiers out of the IRR into TPU status.

Then again, the Army itself is the greatest hurdle to success in the Army.

I thought that was the magic of the IRR. One can be broken all to bits, and unless that is documented in the system for the SM then they are as clean and squeaky as they were Day 1.