How to make consistent jumping with CharacterController

I have a jumping system that jumps for a few seconds (or until key is released), but everytime I run the game the maximum height changes, as well as the jumping speed. Sometimes the player barely jumps, sometimes it jumps a lot and sometimes it jumps how it should. Here's the full code:

 public class player : MonoBehaviour
 {
     [SerializeField] private float speed;
      Vector3 moveVector;
      public CharacterController controller;
      float jumpHeight = 10.0f;
      float gravityValue = -9.81f;
      public float jumpTime;                 //how long has player jumped
      public float jumpTimer = 0.45f;  //how long to jump
      public float jumpSpeed = 0.8f;    //how fast should player jump
      public float gravity = 55.0f; 
     bool right = true;
     public bool running = false;
     public bool falling;
     public bool jumping;
     public bool canRun;
 
     public Animator animator;
     enum ButtonState{Released,Held};
      ButtonState previousButtonState;
 
      public bool CanJump
      {
     get
     {
         return controller.isGrounded && previousButtonState == ButtonState.Released;
     }
      }
      public bool CanContinueJump
      {
     get
     {
         return jumpTime <= jumpTimer && controller.isGrounded == false;
     }
      }
      
 
     void Start()
      {
          controller = GetComponent<CharacterController>();
      }
 
     void Update()
     {
     //REeset the MoveVector
          moveVector = Vector3.zero;
  
     //jump system     
     if(controller.isGrounded == true) jumpTime=0f;
      bool jumpButtonPressed = Input.GetKey(KeyCode.Z);    
     if(jumpButtonPressed )
         {
         if (CanJump || CanContinueJump)
         {
             moveVector.y = jumpSpeed/3;
             jumpTime += Time.fixedDeltaTime;
         }
         }
  
          moveVector.y = moveVector.y - (gravity * Time.fixedDeltaTime);
          controller.Move(moveVector * Time.deltaTime);
 
 // right and left movement
          if(Input.GetKey(KeyCode.RightArrow) ) Move(speed);
          if(Input.GetKey(KeyCode.LeftArrow) ) Move(-speed);
 
 //For animator when running
      if( (Input.GetKey(KeyCode.LeftArrow) || Input.GetKey(KeyCode.RightArrow)) && canRun==true )
         running = true;
      if( (Input.GetKeyUp(KeyCode.LeftArrow) || Input.GetKeyUp(KeyCode.RightArrow))  )
         running = false;
 
 //for animator when jumping
      if( Input.GetKey(KeyCode.Z) && CanContinueJump )
      {
         jumping = true;
         canRun = false;
      } else
      if( Input.GetKey(KeyCode.Z) && controller.isGrounded == false)
       {
         jumping = false;
         falling = true;
      } else if( controller.isGrounded == false)
      {
         jumping = false;
         falling = true;
         canRun = false;
      } else
      {
         jumping = false;
         falling = false;
         canRun = true;
      }
 
     animator.SetBool("running", running);
     animator.SetBool("jumping", jumping);
     animator.SetBool("falling", falling);
 
     previousButtonState = jumpButtonPressed ? ButtonState.Held : ButtonState.Released;
          
     
     }
 
     void Move(float velocity) //move left or right
     {
     if(velocity <0 && right == true)
     {
         transform.Rotate(new Vector3(0.0f, 180.0f, 0.0f) );
         right = false;
     }
     if(velocity > 0 && right == false)
     {
         transform.Rotate(new Vector3(0.0f, 180.0f, 0.0f) );
         right = true;
     }
     transform.position += Vector3.right * velocity * Time.deltaTime;
     }
 }

I tried using deltaTime and fixedDeltaTime, but both have the same issue with jumping.