Jump while running not faster than normal jump. Any help with the code?

Hi everyone!

I found and adapted this piece of code to create a simple character controller. Everything works as I need except for jump: if the character walks (or stands still) and then jump there are no problems but if I make it run and then press the jump button, the jump movement is identical to when it walks. I expect him to have a longer and faster jump but it doesn't happen!

Here's the code (please ignore everything related to the animator):

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerControllerMouseNOROOT : MonoBehaviour
 {
 public CharacterController controller;
 private Animator anim;
 private float x = 0.0f;
 private float z = 0.0f;
 
 [SerializeField] private float walkSpeed = 2.0f;
 [SerializeField] private float runSpeed = 6.0f;
 [SerializeField] private float jumpHeight = 3.0f;
 [SerializeField] private float rotSpeed = 4.0f;
 
 private float speed = 0.0f;
 private float rotation = 0.0f;
 
 [SerializeField] private Transform groundCheck;
 [SerializeField] private float groundDistance = 0.4f;
 [SerializeField] private LayerMask groundMask;
 public bool isGrounded;
 [SerializeField] private float gravity = -19.62f;
 private Vector3 velocity;
 
 // Start is called before the first frame update
 void Start()
 {
 controller = GetComponent<CharacterController>();
 anim = GetComponent<Animator>();
 }
 
 // Update is called once per frame
 void Update()
 {
 // Check to see if player is grounded
 isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);
 
 if (isGrounded && velocity.y < 0)
 {
 velocity.y = -2.0f;
 anim.SetBool("isGrounded", true);
 }
 
 // Player movement and sprint
 x = Input.GetAxis("Horizontal");
 z = Input.GetAxis("Vertical");
 rotation = x;
 anim.SetFloat("Rotation", rotation);
 
 if (z != 0f)
 { 
 if (z > 0)
 {
 speed = walkSpeed;
 anim.SetFloat("Speed", 1.0f);
 }
 else
 {
 speed = walkSpeed;
 anim.SetFloat("Speed", -1.0f);
 }
 
 if (Input.GetButton("Sprint") && isGrounded && z > 0)
 {
 speed = runSpeed;
 anim.SetFloat("Speed", 2.0f);
 }
 }
 else
 {
 speed = 0f;
 anim.SetFloat("Speed", 0f);
 }
 
 Vector3 move = Vector3.Normalize(transform.right * x + transform.forward * z);
 
 move *= speed;
 
 velocity.y += gravity * Time.deltaTime;
 
 controller.Move(move * Time.deltaTime);
 
 controller.Move(velocity * Time.deltaTime);
 
 transform.Rotate(0, x * rotSpeed, 0);
 
 // Jump
 if (Input.GetButtonDown("Jump") && isGrounded)
 {
 isGrounded = false;
 velocity.y = Mathf.Sqrt(jumpHeight * -2f * gravity);
 anim.SetTrigger("isJumping");
 anim.SetBool("isGrounded", false);
 }
 
 }
 
 }

Thank you in advance for your help!