I was replacing the front door speaker on the passenger side. I removed all the fasteners retaining the door panel and pulled it off, unplugged the connections and temporarily set it back in place. Later I came back and started to remove the door panel and noticed this piece laying in the storage bin in the bottom of the door panel. It's possible it's been there since I bought the truck I guess, or it came off the door panel, or less likely the A-pillar trim, since I replaced the tweeter before working on the door.

 

Open the right door, and compare trim pieces...

 

This!

And a tip for the future. I've gotten into the habit of keeping my phone out and snapping pictures as I do any tear down work on a vehicle. Especially helpful when doing wiring or unplugging a bunch of connectors in the dash. Amazing how many times I end up with one or two things that I'm trying to guess where they were on reinstall. Having pics to look back has saved me more than once. I miss the days of not having a zillion clips, hangers, snaps, etc., to remove just to get to the two or three bolts needed to fix something.

 

Looks like a door guard that goes on the side of the door to prevent you damaging the door when opening against a hard surface like Brick.

 

Excellent advise Nuke83! I go a step further, keep a digital camera on hand. Shoot reference photos galore, save them on my computer for future projects mine of friends. Since the adoption of digital photography my camera hobby took a huge step. Nice not to worry about the time and cost of photo development! KM