How to slow player on x and z

Hey,

As Harinezumi commented, your velocity limitations are usefull when the character isn't falling. So try to detect when the character is falling and then turn off the limitation. Maybe try to look if your character is grounded instead of look for his Y velocity (he may be going down a hill)

 if(character.isGrounded)
 {
     LimitateVelocity = true;
 }else
 {
     LimitateVelocity = false;
 }

something like that maybe. Cheers!