Jump not working with Time.deltaTime

I am trying to make my code so that when the character jumps it's not jumping way higher when the FPS is low. I can not see anywhere that the deltaTime is not being properly calculated so I can't make sense of it.

I have truncated the code to the relevant parts for jumping. I would very much appreciate any help. Thank you.

 using UnityEngine;
 using System.Collections;

 [RequireComponent(typeof(CharacterController))]
 public class PlayerMovement : MonoBehaviour
 {
     public float jumpSpeed = 15.0f;
     public float jumpHeight = 30.0f;
     public float gravity = 21.0f;
     
     public enum FallingState { Grounded, Falling, Jumping }
     public FallingState fallingState;

     private Vector3 hMoveDirection;
     private float vMoveDirection;
     private float vVelocity;
     private CharacterController characterController;
     private Animator animator;
     private float deadZone = 0.2f; // dead-zone for joysticks

     void Awake()
     {
         characterController = gameObject.GetComponent<CharacterController>();
         animator = gameObject.GetComponentInChildren<Animator>();
     }

     void Update()
     {
         /* Process Vertical Movement */
         switch(fallingState)
         {
             case FallingState.Grounded:
                 vVelocity = 0.0f;
                 break;
             case FallingState.Falling:
                 vMoveDirection -= gravity * Time.deltaTime;
                 break;
             case FallingState.Jumping:
                 if (vVelocity >= jumpHeight)
                 {
                     fallingState = FallingState.Falling;
                     vVelocity = 0.0f;
                 }
                 else
                 {
                     vMoveDirection = jumpHeight - vVelocity;
                     vVelocity += jumpSpeed * Time.deltaTime;
                 }
                 break;
         }
         
         if (characterController.isGrounded && fallingState != FallingState.Jumping)
         {
             fallingState = FallingState.Grounded;
             if (Input.GetButton("Jump") || jumpButton.buttonState == EasyButton.ButtonState.Press)
                 fallingState = FallingState.Jumping;
         }
         else if(fallingState != FallingState.Jumping)
             fallingState = FallingState.Falling;


             /* Process Character Translation */
         Vector3 moveDirection = transform.forward * moveSpeed * hMoveDirection.z;
         moveDirection.y = vMoveDirection;
         characterController.Move(moveDirection * Time.deltaTime); // move character
         
         /* Process Character Rotation */
         transform.Rotate(new Vector3(0.0f, 1.0f, 0.01f), hMoveDirection.x * calcTurnSpeed * 20.0f * Time.deltaTime);
     }
 }