Toyotero
Explorer
If im right, it's due to the fact that its Body on Frame construction. What you're actually seeing is the body move in reference to the frame staying rock solid. If you we're to try to move the bumper when it's stopped, it would not budge. My FJ ARB bumper does the same thing. I've had zero problems.
Righto, body mount bushings doing their job more than bumper movement makes sense.
btw, I didn't mean to indicate that it might be a problem, just interesting to see since it isn't something you typically get to see in person or even in a video.