It even got the wife to comment, so it was a significant drop, not a gradual process.
1) Checked to make sure the lamp setting on the PJ is still "High"
2) Looked at the indicator lamp. It seems to flash faster now when I turn the PJ off for the first half of the cool down cycle (i.e. 2 flashes/sec for the first minute or so, then down to 1 flash/sec until it goes off completely). These are green flashes. All of the diagnostics in the manual discuss red flashes for error conditions.
3) I've not yet removed/cleaned the filters, but I've seen no warnings either. The manual indicates filter cleaning at 1500 hours... I have only 1/3rd of that on the PJ in a non-dusty environment.