Not gonna pretend I'm a 60' guru but if you slow the video down you have 5 almost 6 sidewall wrinkles. I've always been told 2-2.5 and any more the tire is wadding up and acting like a spring. If you watch, that's what I'm seeing, the tire wads up, and releases momentarily and initiates the bucking. Even as big as those are, I'd be going the other direction in PSI. I think you're trying to compensate some other issue by continuing to drop pressure.