player is shake up-down?

my player is shake when it reach 100 position on y axis,i mean it was going to 101 and 100 postion(up down) continuously.Here my script.

 temppos = transform.position;
             if (temppos.y > 100f && temppos.y < 110f) {
                 temppos.y = Mathf.Clamp (temppos.y, -maximum_up, maximum_up);
                 //temppos.y = 100f;
                 transform.position = temppos;
             }
 if (_slider.value > 3f) {
  if (transform.position.y < maximum_up) {
   if (transform.rotation != Quaternion.Euler (0, 0, 0)) {
             transform.localPosition += transform.up * Time.deltaTime * _slider.value * forward_speed;
 } else {
 transform.localPosition += transform.up * Time.deltaTime * _slider.value;
 }
 } else
 {
 if (transform.rotation.eulerAngles.x > 100f) {
         transform.localPosition += transform.up * Time.deltaTime * _slider.value * forward_speed;
 } 
 else if (transform.rotation.eulerAngles.x > -100f && transform.rotation.eulerAngles.x < -80f) {
 transform.localPosition += transform.up * Time.deltaTime * _slider.value * forward_speed;
 }
  else if (transform.rotation.eulerAngles.z > 100f) {
 transform.localPosition += transform.up * Time.deltaTime * _slider.value * forward_speed;
 } 
 else if (transform.rotation.eulerAngles.z > -100f && transform.rotation.eulerAngles.z < -80f)
  {
 transform.localPosition += transform.up * Time.deltaTime * _slider.value * forward_speed;
     }
     }
 }

Maximumup = 100;