Character Controller continues moving upwards on slopes after horizontal movement has stopped

I'm one step away from getting the right feel for my character controller- I have an issue that kind of caused me to stop game development for a while but I really want to get it out of the way and move onto the cool stuff in my game.

I've included a video link that demonstrates the problem: https://youtu.be/_WNIqz6dbfQ

As you can see, the player ascends the slope as intended, but once the movement keys are released, the player does a little bit of a "bump" upwards, falls back down, and if you watch closely, you'll see that they also slowly ascend upwards for a short time before falling back down. If I can eliminate this bump and the little bit of levitation at the end I will be happy with what I have.

 using UnityEngine;
 
 public class moveTest : MonoBehaviour
 {
     //Essentials
     [SerializeField] private GameObject playerObject;
     [SerializeField] private GameObject playerModel; 
     [SerializeField] private Camera playerCamera;
     private CharacterController playerController;
     
 
     private Vector3 playerVelocity; 
     private Vector3 moveDirection; 
 
     private float minimumSpeed = 0.1f;
     private float gravityForce = 25f; 
     private float terminalVelocity = -25f; 
     private bool grounded = true; 
     private float accelerationSpeed = 100f;   
     float frictionOffset = 94.42f; 
 
 
     LayerMask playerCollisionLayer = (1 << 6) | (1 << 7) | (1 << 0);
 
     double mouseSensitivity = 1;
     bool invertY = true;
 
     private int fieldOfView = 90; 
 
     KeyCode moveForward = KeyCode.W;   
     KeyCode moveBack = KeyCode.S;   
     KeyCode moveLeft = KeyCode.A;   
     KeyCode moveRight = KeyCode.D;   
 
     KeyCode lookUp = KeyCode.UpArrow;   
     KeyCode lookDown = KeyCode.DownArrow;   
     KeyCode turnLeft = KeyCode.LeftArrow;   
     KeyCode turnRight = KeyCode.RightArrow; 
 
     KeyCode crouch = KeyCode.X;
     KeyCode jump = KeyCode.Space;
     KeyCode use = KeyCode.E; 
     KeyCode flashLight = KeyCode.L; 
 
     KeyCode primaryFire = KeyCode.Q; 
     KeyCode secondaryFire = KeyCode.Mouse1; 
     KeyCode ability = KeyCode.F; 
     KeyCode ability2 = KeyCode.V; 
     KeyCode ability3 = KeyCode.C; 
 
     KeyCode reload = KeyCode.R; 
 
     KeyCode console = KeyCode.Tilde; 
     KeyCode quickSave = KeyCode.F6; 
     KeyCode quickLoad = KeyCode.F9; 
     KeyCode openChat = KeyCode.Slash; 
     KeyCode levelView = KeyCode.Minus; 
 
     
     
     private void controlMouse()
     {
         float mouseX = Input.GetAxisRaw("Mouse Y");
         float mouseY = Input.GetAxisRaw("Mouse X"); 
         
         if (Input.GetKey(lookUp)) 
         {
             mouseX -= 90f * Time.deltaTime;
         }
         if (Input.GetKey(lookDown))
         {
             mouseX += 90f * Time.deltaTime;
         }
         if (Input.GetKey(turnLeft))
         {
             mouseY -= 90f * Time.deltaTime;
         }
         if (Input.GetKey(turnRight))
         {
             mouseY += 90f * Time.deltaTime;
         }
 
         playerModel.transform.eulerAngles += new Vector3(0, mouseY, 0);
         playerCamera.transform.eulerAngles += new Vector3(mouseX, mouseY, 0);
     }
 
     private void handleInput() 
     {
 
 
         moveDirection = Vector3.zero; 
 
         
         if (Input.GetKey(moveForward))
         {
             moveDirection += playerModel.transform.forward;
         }
         if (Input.GetKey(moveBack))
         {
             moveDirection -= playerModel.transform.forward;
         }
         if (Input.GetKey(moveLeft))
         {
             moveDirection -= playerModel.transform.right;
         }
         if (Input.GetKey(moveRight))
         {
             moveDirection += playerModel.transform.right;
         }
 
         if(Input.GetKey(jump) && isPlayerGrounded() && playerVelocity.y < 10f)
         {             
             playerVelocity.y = 10f;
         }
 
         if (Input.GetKey(crouch))
         {
             //not yet implemented.  
         }
         moveDirection = moveDirection.normalized;
         
         playerVelocity += moveDirection * accelerationSpeed * Time.deltaTime; 
 
         if (Input.GetKey(use))
         {
 
         }
         playerController.Move(playerVelocity * Time.deltaTime);
     }
 
     
     private void applyPhysics() 
     {
         Vector3 tempVelocity = playerVelocity;
         tempVelocity.y = 0;
 
         tempVelocity *= Time.fixedDeltaTime * frictionOffset;
 
         playerVelocity.x = tempVelocity.x;
         playerVelocity.z = tempVelocity.z;
         if (playerVelocity.y > terminalVelocity) 
         {
             if(!isPlayerGrounded())
             {
                 playerVelocity.y -= Time.fixedDeltaTime * gravityForce;
             }
             if(isPlayerGrounded())
             {
                  //not sure what to do here- something could be placed here to eliminate the bump.  
             }
 
         }
 
 
         if (playerVelocity.z < minimumSpeed && playerVelocity.z > -minimumSpeed) { playerVelocity.z = 0; }
         //if (Mathf.Abs(playerVelocity.z) < minimumSpeed ) { playerVelocity.z = 0; }
         if (playerVelocity.x < minimumSpeed && playerVelocity.x > -minimumSpeed) { playerVelocity.x = 0; }
     }
 
 
     private bool isPlayerGrounded()
     {
         Vector3 center = new Vector3(this.transform.position.x, this.transform.position.y - 1f, this.transform.position.z);
         Vector3 size = new Vector3(0.35f, 0.1f, 0.35f);
 
         if (Physics.CheckBox(center, size, new Quaternion(), playerCollisionLayer))
         {
             return true;
         }
         else
         {
             return false;
         }
     }
 
 
 
 
     private void OnControllerColliderHit(ControllerColliderHit collision) 
     {
         Vector3 collisionDifference = collision.normal * Vector3.Dot(playerVelocity, collision.normal);
         playerVelocity -= collisionDifference;
     }
 
 
     void Start()
     {
         //Application.targetFrameRate = 30;
 
         playerObject = this.gameObject;
         playerController = playerObject.GetComponent<CharacterController>();
         playerCamera = playerObject.GetComponentInChildren<Camera>();
     }
 
     private void FixedUpdate()
     {
         applyPhysics();
     }
 
     void Update()
     {
         print(playerVelocity);
 
         controlMouse();
         handleInput();
     }
 }

I feel like I've tried everything there is to try- why is this happening and what can I change in my code in order to prevent it / fix it?