character wont rotate and is stuck to the one position.

my character will not rotate left and right when i press the arrow keys. i am trying to get my character on a skateboard to go up a ramp and rotate with the ramp so i managed to get the raycast working correctly but then this happened so i think its something to do with the ray cast. as well when i take out the Vector3.slerp it doesnt rtate with the ramp but i can rotate left and right. here is my code

 var rotateSpeed = 90;
 var pushingImpulse = 3.5;
 var maxSpeed = 12;
 var decayRate = 0.1;
 
 var targetDir:Vector3;
 var ray:Ray;
 var hit:RaycastHit;
 
 
 private var character : CharacterController;
 private var trans : Transform;
 private var speed = 0.0;
 
 function Start ()
 {
     character = GetComponent(CharacterController);
     trans = transform;
 }
 
 function Push()
 {
     speed += pushingImpulse;
     speed = Mathf.Min(speed, maxSpeed);
 }
 
 function Update ()
 {
     var horizontal = Input.GetAxis("Horizontal");
     trans.Rotate(0, rotateSpeed * horizontal * Time.deltaTime, 0);
     
     if (character.isGrounded && Input.GetKey(KeyCode.UpArrow))
         Push();
         
     var moveDirection = trans.forward * speed;
     moveDirection += Physics.gravity;
     character.Move(moveDirection * Time.deltaTime);
     
 
     //Inside the Update function
 //Cast the ray relative to player
 ray = Ray(trans.position + Vector3.up, Vector3.down);
  
 //If we are on the ground and we get a raycasthit
 if (Physics.Raycast(ray, hit, 100)) {
     if (character.isGrounded) {
         targetDir = hit.normal;
         Debug.DrawLine (transform.position, hit.point, Color.green);
         
     }
 }
  
 //Smoothly move towards the new direction
 transform.up = Vector3.Slerp(transform.up, targetDir, 5 * Time.deltaTime);
     
     
   
     if (character.isGrounded)
     {
         speed -= decayRate * Time.deltaTime * speed;
     }  
 }