There are two thick felt like panels on the back of the cab between the the cab and the bed of these trucks. (I assume it is to reduce the vibration in this area) One of mine is falling down. They are not the air vents but located above the air vents and somewhat L shaped.

2019 F150 Super Crew Cab, build in June 2019, 5.0 engine 5.5 bed.

 

I’ve read a similar post, but it was a while back.
If it’s the part I’m thinking of, I believe the consensus was that they are there for aerodynamics....they block air from coming up through there.

 

I always figured those were used during assembly to prevent cab/bed contact. Had no idea they served a purpose otherwise. Sorry that I can't help with part ID.

 

Okay, I found an article that mentions it.
.

• Cargo box is narrower than the cab, with no reduction in box volume, which enhances airflow, while a trim piece prevents air from getting trapped between cab and box

Here is the short article from Ford about aerodynamic improvements to the 2015 F150, which is when they added this item.
https://media.ford.com/content/fordm...amic-drag.html


edited to add:
Robbgt, you could also be correct. There is another piece of trim that goes across the gap at the bottom of the bed where it meets the cab. Either or both of these items could help improve aerodynamics, reduce road noise, or help keep the bed from hitting the cab during assembly. Maybe both items do all three things at the same time, rather than serving a single purpose.

 

After speaking with the Ford parts manager, he was able to identify the part as a Sound Insulator, part number FL3Z-1540381. I am now seeing if the Service department will replace it under warranty. He found the part under the Other Body Hardware tab on his parts software.

 

Glad you were able to identify - thanks for circling back with a post.

 

Service Advisor called me and said that Ford will replace the insulators under warranty. Will be done in the body shop as the bed has to be moved or removed.