Is the air filter clean?

Very much so, CC. Just replaced no more than 3,000 miles ago and put in an STP higher-grade filter.
But now you've got me wondering if the high-grade filter is possibly restricting air flow. I don't recall any mention of this code previously.

A quick follow up here.

Interestingly enough, my scans today have no longer thrown a DTC P0172. Once the scanner links it immediately reads the VIN correctly, lists out the year, make, model correctly then goes through a few additional questions. First one is whether it has an air pump; I've always responded yes or "with air pump" and received the code. The first time I answered "without air pump" the P0172 code went away. I then disconnected the tool, reconnected, answered "with air pump" again and the P0172 didn't reappear. I did nothing in the interim to manually clear the codes. So, at this point, I'm uncertain what is going on and not sure whether I should feel good about not getting a code.

Anyway, so now that I've invested in the scan tool, what live data should I stream so when the 2nd gear shifts intermittently start again I will have captured the right data for an appropriate diagnosis? I can run all sorts of data on the automatic transaxle (AT), engine controls, etc. Inside the AT, it will read 1-2 shift time, 1-2 solenoid, 2-3, 3-4, transmission fluid temperature, input/output shaft speed, etc.

Thank you.

No, the clean STP filter shouldn't be an issue.

Keep an eye on it for a while and see what happens.

If you can watch commanded ratio, actual ratio, and any transmission fluid pressure readings, that would be a help.