Rigidbody Climbing up stairs not working

Hello I'm trying to make an FPS game, and I want to use Rigidbody for my movement it works really well and all, but there's one problem, Climbing upstairs doesn't work properly, It works when you get a head start but if you move slow enough you cant climb up the stairs. I don't really care if it doesn't look natural and also I get stuck on walls when pressing forward in mid-air facing a wall a=I made a cod and watched some tutorials but it doesn't work, It work previously but when I added shooting it stopped working I don't know if this is already answers but some help would be appreciated thx.

[RequireComponent(typeof(Rigidbody))]       public class PlayerController : MonoBehaviour {

  [Header("Player")]
  public float stairsWidth = 1.2f;
  [Range(0.1f, 10f)]
  public float smoothTime = 5f;
  public float maxStepHeight = 1;
  public int stairDetail = 15;
  public float moveSpeed = 1200;
  public float jumpForce = 300;
  public float groundDist = .4f;
  [Header("Camera")]
  public float mouseSensitivity = 100f;
  float xRotation;
  [Header("Refrences")]
  public Transform groundCheck;
  public LayerMask ground;
  public Camera cam;
  Rigidbody rb;
  Vector3 smoothVelocity;
  bool grounded = false;
  bool isFirstCheck = false;
  bool canMove = true;
  // Start is called before the first frame update
  void Start()
  {
      rb = GetComponent<Rigidbody>();
      Cursor.lockState = CursorLockMode.Locked;
  }
  // Update is called once per frame
  void Update()
  {
      //Checks if is on the ground
      grounded = Physics.OverlapSphere(groundCheck.position, groundDist, ground).Length > 0;
      if (grounded && Input.GetButtonDown("Jump"))
      {
          rb.AddForce(Vector3.up * jumpForce);
      }
      //moves
      Vector2 xMov = new Vector2(Input.GetAxisRaw("Horizontal") * transform.right.x, Input.GetAxisRaw("Horizontal") * transform.right.z);
      Vector2 zMov = new Vector2(Input.GetAxisRaw("Vertical") * transform.forward.x, Input.GetAxisRaw("Vertical") * transform.forward.z);
      Vector2 velocity = (xMov + zMov).normalized * moveSpeed * Time.deltaTime;
      //climb stairs or slopes
      isFirstCheck = false;
      canMove = true;
      for (int i = stairDetail; i >= 1; i--)
      {
          Collider[] c = Physics.OverlapBox(transform.position + new Vector3(0, i * maxStepHeight / stairDetail - transform.localScale.y, 0), new Vector3(stairsWidth, maxStepHeight / stairDetail / 2, stairsWidth), Quaternion.identity, ground);
          if (velocity.x > 1f && velocity.y > 1f)
          {
              print(c.Length > 0);
              if (c.Length > 0)
              {
                  if (i == stairDetail)
                      isFirstCheck = true;
                  if (!grounded)
                  {
                      canMove = false;
                  }
                  if (!isFirstCheck)
                  {
                      transform.position += new Vector3(0, i * maxStepHeight / stairDetail, 0);
                  }
              }
          }
      }
      if (canMove)
      {
          rb.velocity = Vector3.SmoothDamp(rb.velocity, new Vector3(velocity.x, rb.velocity.y, velocity.y), ref smoothVelocity, smoothTime * Time.deltaTime);
      }
      //Rotates camera
      float mouseX = Input.GetAxisRaw("Mouse X") * mouseSensitivity * Time.deltaTime;
      float mouseY = Input.GetAxisRaw("Mouse Y") * mouseSensitivity * Time.deltaTime;
      xRotation -= mouseY;
      xRotation = Mathf.Clamp(xRotation, -90f, 90f);
      rb.rotation *= Quaternion.Euler(Vector3.up * mouseX);
      cam.transform.localRotation = Quaternion.Euler(xRotation, 0f, 0f);
  }

}