Character controller jittering up and down

Hi people of the internet. I have an issue where my character jitter up and down when moving. I use the following code to control it (third person controller) on a character with a capsule collider and despite my efforts the jitter just wont stop. I tried changing the position of the gravity calculation but nothing.Its quite annoying. Please tell me the way to smooth movement.

     private void Update()
     {
         GetInput();
         CalculateDirection();
         CalculateForward();
         RaycastGround();
 
         if (Input.GetButtonDown("Jump"))
         {
             Jump();
         }
 
     }
 
     private void FixedUpdate()
     {
         if (m_Input != Vector3.zero)
         {
             m_Animator.SetBool("IsMoving", true);
             Rotate();
             SetSpeed();
         }
         else
         {
             m_Animator.SetBool("IsMoving", false);
             ResetSpeed();
         }
 
         m_MoveDir = m_Forward * m_CurrentSpeed;
         m_MoveDir.y = m_RigidBody.velocity.y;
 
         if (m_RigidBody.velocity.y > 1)
         {
         }
         m_MoveDir.y -= m_FakeGravity * Time.fixedDeltaTime;
         m_RigidBody.velocity = m_MoveDir;
     }
 
     private void GetInput()
     {
         m_Input.x = Input.GetAxis("Horizontal");
         m_Input.z = Input.GetAxis("Vertical");
     }
 
     private void CalculateDirection()
     {
         m_RotationAngle = Mathf.Atan2(m_Input.x, m_Input.z);
         m_RotationAngle *= Mathf.Rad2Deg;
         m_RotationAngle += m_Camera.eulerAngles.y;
     }
 
     private void CalculateForward()
     {
         m_Forward = transform.forward;     
     }
 
     private void RaycastGround()
     {
         m_IsGrounded = Physics.Raycast(transform.position, Vector3.down, out m_HitInfo, m_CharacterHeight + m_HeightPadding, m_WalkLayer);
     }
 
     private void Rotate()
     {
         m_TargetRotation = Quaternion.Euler(0f, m_RotationAngle, 0f);
         transform.rotation = Quaternion.Slerp(transform.rotation, m_TargetRotation, m_TurnSpeed * Time.fixedDeltaTime);
     }
 
     private void SetSpeed()
     {
         if (m_CurrentSpeed < m_RunSpeed)
         {
             m_CurrentSpeed += m_RunSpeed * (m_RunAcceleration * Time.fixedDeltaTime);
         }
         else
         {
             ResetSpeed();
         }
     }
 
     private void Jump()
     {
         if (m_IsGrounded)
         {
             m_IsGrounded = false;
             m_RigidBody.AddForce(transform.up * m_JumpForce);
         }
     }
 
     private void ResetSpeed()
     {
         m_CurrentSpeed = 0f; 
     }