A good First Person Jumping System

I am very new and I've made a few attempts at making a FPS character controller. Each time I've been stumped by jumping, watched a lot of tutorials and all of them seam to have this same issue. The jump is inconsistent, it wont work every time the button is pressed and it wont be a consistent amount of force applied even when though its looking for when the button is pressed down. This has really baffled me, so if you could point me in the direction of a tutorial that works for you or help with code.

Code (CSharp):

1. public class ControlInput : MonoBehaviour
2. {
3.  
4.     public CharacterController playerObj;
5.  
6.     #region PUBLIC FIELDS
7.     [Header(header: "PlayerMovement")]
8.     public float playerSpeed = 12f;
9.     public float JumpForce = 10;
10.     public float maxChangeInVerticalVelocity = 100;
11.  
12.     [Header(header: "Player Environments")]
13.     public float gravity = -9.81f;
14.  
15.     [Header(header: "Leaning While Running")]
16.     public Transform _Pivot;
17.     public float RunningLeanspeed = 10f;
18.     public float RunningLeanmaxAngle = 2f;
19.     #endregion
20.  
21.     float curAngle = 0f;
22.  
23.     Vector3 velocity;
24.     int jumpCount = 0;
25.  
26.     // Update is called once per frame
27.  
28.     void Awake()
29.     {
30.         if (_Pivot == null && transform.parent != null) _Pivot = transform.parent;
31.     }
32.     void Update()
33.     {
34.         float x = Input.GetAxis("Horizontal");
35.         float z = Input.GetAxis("Vertical");
36.  
37.         Vector3 move = transform.right * x + transform.forward * z;
38.  
39.  
40.        
41.  
42.         //RUNNING LEAN
43.         if (Input.GetKey(KeyCode.A))
44.         {
45.             curAngle = Mathf.MoveTowardsAngle(curAngle, RunningLeanmaxAngle, RunningLeanspeed * Time.deltaTime);
46.         }
47.         else if (Input.GetKey(KeyCode.D))
48.         {
49.             curAngle = Mathf.MoveTowardsAngle(curAngle, -RunningLeanmaxAngle, RunningLeanspeed * Time.deltaTime);
50.         }
51.         else
52.         {
53.             curAngle = Mathf.MoveTowardsAngle(curAngle, 0f, RunningLeanspeed * Time.deltaTime);
54.         }
55.  
56.         _Pivot.transform.localRotation = _Pivot.transform.localRotation * Quaternion.AngleAxis(curAngle, Vector3.forward);
57.         curAngle = Mathf.Clamp(curAngle, -5f, 5f);
58.  
59.         //JUMPING
60.         if (Input.GetKeyDown(KeyCode.Space))
61.         {
62.             velocity.y += JumpForce;
63.         }
64.         else
65.         {
66.             velocity.y += gravity * Time.deltaTime;
67.         }
68.  
69.      
70.  
71.         //EDITING THE ACTUAL PLAYER
72.  
73.         playerObj.Move(move * playerSpeed * Time.deltaTime);
74.         playerObj.Move(velocity * Time.deltaTime);
75.  
76.  
77.     }
78. }
79.  

Cheers for anyhelp