The character controller stop moving when the Speed Start increase Endless runner

this is the class for player movement

using UnityEngine; using System.Collections;

public class PlayerMotor : MonoBehaviour {

  private CharacterController controller;
  private Vector3 moveVectore;
  private float animationDuration = 0.2f;
  public float speed = 0.01f;
  private float verticalVelocity = 0.0f;
  public float gravity = 12.0f;
  public float jumpForce = 20.0f;
  public float speedH = 20f;
  private Vector3 left = new Vector3(-4, 0, 0);
  private Vector3 right = new Vector3(4, 0, 0);
  private bool isDeath = false;
  void Start()
  {
      controller = GetComponent<CharacterController>();
   
  }
  void Update()
  {
      if (isDeath)    
      
          return;  
      
      if (Time.time < animationDuration)
      {
          controller.Move(Vector3.forward * speed * Time.deltaTime);
          return;
      }
      if (controller.isGrounded)
      {
          verticalVelocity = -gravity * Time.deltaTime;
          if (Input.GetKeyDown(KeyCode.Space))
          {
              verticalVelocity = jumpForce;
          }
      }
      else
      {
          verticalVelocity -= gravity * Time.deltaTime;
      }
      Vector3 moveVector = Vector3.zero;
      //X
     
      if (Input.GetKeyDown("left"))
      {
          controller.Move(left);
      }
      if (Input.GetKeyDown("right"))
      {
          controller.Move(right);
      }
      //Y
      moveVector.y = verticalVelocity;
      //Z
      //  moveVector.z = Input.GetAxis("Vertical") * 5.0f;
      
      controller.Move(Vector3.forward * speed);
      controller.Move(moveVector * Time.deltaTime);    // here when i delete this function the character controller is continue the moving , but the jump don't  working
  }
  public void SetSpeed(float modifier)
  {
      speed = 0.5f + modifier;   
  }
  private void OnControllerColliderHit(ControllerColliderHit hit)      
  {
      if (hit.point.z > transform.position.z + controller.radius)
          Death();
  }
  private void Death()
  {
      isDeath = true;
      GetComponent<Score>().OnDeath();    
  }

}

and this class for Score

using UnityEngine; using System.Collections; using UnityEngine.UI;

public class Score : MonoBehaviour {

  private float score = 0.0f;
  public Text scoreText;
  public float difficultyLevel = 1f;
  private float maxDifficultyLevel = 2;
  private float scoreToNextLevel = 2;
  private bool isDead = false;
  // Update is called once per frame
  void Update ()
  {
     if (isDead)  
          return;
      if (score >= scoreToNextLevel)
          LevelUp();
      
      score += Time.deltaTime;
      scoreText.text = ((int)score).ToString();
  
  }
  void LevelUp()
  {
     
      if (difficultyLevel == maxDifficultyLevel)
      {
          return;
      }
     // scoreToNextLevel *= 2f;
      difficultyLevel+=0.1f;   
      GetComponent<PlayerMotor>().SetSpeed(difficultyLevel);  
  }
  public void OnDeath()
  {
      isDead = true;
  }

}

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