After watching again, it does only seem to happen on the 1st to 2nd shift. So over-gearing of 2nd makes sense. The initial high rev could then be from the flywheel and other rotating mass keeping momentum and finally getting dragged down.
I am relatively new to this. I can observe reasonably well but fixing things is a different story (just watch my driving. I can tell you every place I screw up yet in the next video, the mistakes are not completely fixed. Meh. Still having fun).
Have you looked at the mathematical RPM drop for the 1 - 2 shift v. all of the others? That could be informative. I use this link to see the RPM drop.
http://www.auto-ware.com/calcs/gears/gears.htm
Good luck and post more video, I need to learn how to battle in big packs like that and watching is learning.
Eric Little