Question Why is my movement jittery?

I'm sure it's a update vs fixedupdate problem, but I cant figure out why.

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5. public class PlayerMovement : MonoBehaviour
6. {
7.     [SerializeField] float walkSpeed, runSpeed, crawlSpeed, airAcceleration, groundAcceleration, differentialAcceleration, differential, currentSpeed, targetSpeed;
8.     PlayerState playerState;
9.     Rigidbody myRigidbody;
10.     bool isFacingRight;
11.     // Start is called before the first frame update
12.     void Start()
13.     {
14.         isFacingRight = true;
15.         myRigidbody = GetComponent<Rigidbody>();
16.         playerState = GetComponent<PlayerState>();
17.        
18.     }
19.     private void Update()
20.     {
21.         targetSpeed = Input.GetAxis("XMovement");
22.         if (playerState.isCouching) targetSpeed = targetSpeed * crawlSpeed;
23.         if (!playerState.isCouching && !playerState.isRunning) targetSpeed = targetSpeed * walkSpeed;
24.         if (!playerState.isCouching && playerState.isRunning) targetSpeed = targetSpeed * runSpeed;
25.     }
26.     // Update is called once per frame
27.     void FixedUpdate()
28.     {
29.         currentSpeed = targetSpeed;
30.         Vector3 applyMovement = new Vector3(currentSpeed, 0, 0);
31.         applyMovement = applyMovement * Time.fixedDeltaTime;
32.         applyMovement += myRigidbody.position;
33.         myRigidbody.MovePosition(applyMovement);
34.     }
35. }
36.  

I've tried moving the inputs to the fixed update, but it still jitters.

EDIT: It seems to have issues in certain areas, not everywhere. From 0 to 8 on the x plane it jitters, and everything after is smooth.

 

Have you made sure to set your rigidbody to Interpolate?

 

That was it.

Thanks!