Occasional vacuum leak?

This can be a low engine vacuum issue due to a clogged catalytic converter. This would be why the transmission downshifts as well. There are two cats so either one could be partially blocked. If you have a check engine light on or a scanner that can read the long and short trims, we can know more. Also, I would check under the hood for small broken vacuum lines. Please go over these to guides to help find the problem:

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

and

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please go over these guides and get back to us.

Long trims are abt +10% on bank 1, abt +8% on bank 2. Short trims are about 0.

I don't think the cats are partially plugged. Cat Temperatures seem fine.

The harsh downshift seems to only happen when I'm climbing a hill or passing on a freeway, and then only when the transmission is hot from an extended drive.

The HVAC is not stuck in defrost mode. I can switch to center discharge, but volume is frequently low, but not always.

What I really need is the vacuum map for this car. You have posted 210 Explorer maps, but only for the v6. Mine is the v8 with the dual control HVAC.

Short-Term Fuel Trim (STFT) around 0%, This means the oxygen sensors are currently reading things as balanced, and the PCM isn’t making fast corrections.

Long-Term Fuel Trim (LTFT):

+10% on Bank 1

+8% on Bank 2

This means the PCM is adding extra fuel over time because it sees a persistent lean condition on both banks. So, I would clean the MAF.

On the HVAC problem: Yes, I know but the line could have a crack under the hood, I would inspect the supply line from the engine to the firewall. There is also a vacuum reservoir under the hood that should be checked as well. Please upload a video in your response of the problem. Sorry, for some reason they are not showing the vacuum line diagrams. Check out the images (below). Please let us know what happens.

I tested the black and white check valve that serves to vacuum supply to the HVAC and EGR. The check valve seemed to not reliably close when I sucked on the white side. I believe it should close when the engine vacuum is low, and the reservoir should hold the mode vacuum. Motor. I replaced the check valve this morning.

Not having a vacuum pump tool, I just sucked on the line after the check valve that went into the firewall. It seemed to hold a vacuum.

This tells me I must have a vacuum leak in the engine bay before the check valve? This is why I need the vacuum line plot for this engine?

The vacuum reservoir for the v8 engine is not in the engine bay iirc. I think it is behind the passenger side kickplate. Since my mouth suck test seemed to suggest that line and its various branches are good, not sure I need to dismantle anything.

I had cleaned the MAF sensor last year to no effect.
I also did replace the egg vacuum motor last year.

I tested the black and white check valve that serves to vacuum supply to the hvac and egr. The check valve seemed to not reliably close when I sucked on the white side. I believe it should close when engine vacuum is low and the reservoir should hold the mode vacuum.motor. I replaced the check valve this a.m..

Not having a vacuum pump tool, I just sucked on the line after the check valve that went into the firewall. It seemed to hold a vacuum.

This tells me I must have a vacuum leak in the engine bay before the check valve? This is why I need the vacuum line plot for this engine?

The vacuum reservoir for the v8 engine is not in the engine bay iirc. I think it is behind the passenger side kickplate. Since my mouth suck test seemed to suggest that linecand its various branches are good, not sure I need to dismantle anything.

I had cleaned the maf sensor last year to no effect
I also did replace the egg vacuum motor last year

Yes, a bad check valve can cause the problem, did you drive it after to see if the problem is fixed, all HVAC system leak a little bit which is normal.