2014 Ford Mustang — fuel trims are positive at idle and improve with RPM

I wouldn't throw parts yet. Get a real battery/charging test on the 2014 Ford Mustang, not just resting voltage, before blaming a module. That's the branch I'd chase this week. Post the numbers (or the code) and people can get more specific. Your commute and mine probably aren't the same, but the test still applies. I'd rather pay for diagnosis than a second guess-repair.

It did fuel trims are positive at idle and twice this week, both times after sitting. No change in mileage feel. Not interested in a five-hour wait for a shrug.

This is usually cheaper to test than to guess. Two 2014 Ford Mustangs can feel identical and have different causes, so measure before you copy someone else's repair. You'll know quickly if you're on the wrong tree. Had a similar mess a couple years ago and that's what finally sorted it. I'm in no rush to be a hero on it.