Whenever I decelerate hard enough (though still “normal” and not emergency braking or whatever) I feel as if the seat moves in and out of a notch. Anybody else experience this?

I haven't had this happen. I'd take it back to the dealer if you're under warranty, but make sure they hook the wires back up and bolt everything back down properly if they decide to take it apart.

Is it really the seat or is it the seat belt doing it's thing by locking up on hard stops?

*I was about to start a new thread, but the search function lead me here*
I am experiencing the exact same issue as stated by the OP - his description nailed it.

So today I decided to start digging in by first checking the torque on all 4 corner bolts that secure the rails to the chassis. They were nice and tight.

Next I removed the plastic trim that covers the left seat rail next to the driver's door, and moved the seat to the highest position to help expose the mechanisms underneath. I found 6 bolts (circled in red below) along the seat rails, and I checked their torques as well - all good.
I think these are the only fasteners that I can access without really ripping into the seat. I have a warranty so I'll probably let the dealership take it further, if it comes to that...
One thing I'd like to point out is that at this step I grabbed the front and back of the seat and then muscled it along the forward/backward axis to see if I could get a visual of what was actually shifting. It was obvious that the base of the seat rail (black metal) was secure, and the slider portion (silver metallic with yellow arrows) was doing the shifting... This begins to point me towards "I bought a warranty, the dealership owes me".

Does anyone else have any experience or recommendations for this?





PS - When I removed the plastic trim I also found the item pictured below loose. Can anyone identify it? I checked the passenger side and didn't see anything resembling it over there... Thoughts?

In my case, it is undoubtedly something to do with the seat itself. The shifting is felt in the seat bottom and lower back area, and now I have visual evidence

@Kapitanemo I remember this being a topic on the 4runner forum as well... not sure what the resolution was though.. google 4runner driver seat clicking.
One person found a support weld that had snapped and was causing the clicking sound... others were thinking it was the lumbar or seat slide mechanism...a re-weld seemed to be the only fix that permanently solved the issue if I remember.
https://www.toyota-4runner.org/4th-g...vers-seat.html
https://www.toyota-4runner.org/5th-g...ing-sound.html
https://www.toyota-4runner.org/5th-g...d-i-think.html

Has anyone found a solution that doesn’t involve replacing the seat base or welding the tracks?

This just started happening on my gx460 and now I can’t stop rocking back and forth, it’s like a fidget toy in traffic.

is it worn worm gear drive in the electric slider?