Just an FYI, you can set videos to "Unlisted" and only those with the link, or on the site with the video embedded can see it.
What the transmission is doing is slamming in and out of gear. It's like trying to grab a balloon out of the air. Your hand is going to hit it, the balloon is going ot move, then your hand is going to hit it again.
Try the same thing, but this time keep it going in a circle or running it up and down the road (if you can). I will bet once you get some speed out of the truck, this should stop. If not, then there may be an issue with the clutch. Another thing you can try is to loosen your slipper clutch just a touch so that it slips while you are breaking it in. Not slipping a lot, but enough so the trans is locking in gear.
If you do in fact have an issue with the clutch, you can do one of two things. 1. take it back to where you got it and have them swap it out or 2. put a forward only kit into it as suggested before. I like the forward only kit, but I'm a racer and never back up.