I didn't watch the video, I've built some GM 6T40E & 6T45E........The Center Support snap ring is a BEAR!!! The 6L80E/6L90E CS snap ring is also!
HD Locking Snap Ring Pliers don't work very well, I've tried the Kent Moore dealer tool & it's not any better than other much cheaper tools.
I use the pliers to rotate the snap ring away from the problematic free standing lug, Insert a 90 degree awl between the case & snap ring......Then walk it out with a large flat blade.
This snap ring has a TON of installed pressure & takes more pressure to remove it....And will slip off any plier before you clear the case lugs