Multiple issues with custom character (sliding, floating, etc)

Hello developers!
My team and I have been sitting on this problem for a while now and we just can’t figure out the issue.
We have a custom player model, rigged with animations and everything is working, except that it slides around, sometimes glitches into the ground when jumping, and slides off of slopes in the terrain, slowly spinning on slight inclines and more. We’ve tried everything we could find in the forums and videos.

Setting the hipheight does work at about 6, but that also lifts the character off the ground and makes you float. But we want the model to “move with the ground”, like foot planting. Setting it any lower makes it slide around again.
We set everything except the HumanoidRootPart to CanCollide = Off and nothing changed.
I even played around with gravity, hoping it would help.
Video of the hipheight at 6

What is the issue here?