It's a great character controller that is near flawless. If you have the asset try the character playground scene with the ultimate character controller. You'll notice that your controller gets stuck in the geometry and will hiccup on stairs with just basic walking without crouching/jumping/etc...
I would like to replace your character controller's code with the Kinematic Character Controller from the asset store but retain everything else. Is this something that would be a nightmare to try and do?