1. Set your Sprint and Crouch on the same Button/Key (for example, set them both to C)
2. Make sure Sprint and Crouch are set to Hold, not Toggle.
3. While you have stamina and not touching a wall, Walk/Hold backwards (S on keyboard) and press the sprint/crouch combined Key (C, if you set them to C for the example). You need to be walking for this to work, if a wall is in the way you'll reset the glitch.
4. Everytime you slide and use stamina, you are gaining speed; infinitely with each press.
5. That's it. There may be easier/other methods, but this is what I was told. You don't need to spam any inputs for this to work. You also can grab items normally, and keep the same speed the next time you use the crouch slide. You only lose the glitch if you reset it.
To reset/stop the super slide glitch, either jump and press the sprint/crouch key or back up into a wall and press the sprint/crouch key.
You can do this WITHOUT setting sprint and crouch to the same key, but it's basically a TAS only technique at that point.
Credit goes to AquaBolt for telling me about the glitch and trying to explain it to me.