Stuttering with moving Rigidbody

Hi! My name is Raúl.
First of all, sorry for my english.

I am getting a lot of stuttering when moving my character with rigidbody.MovePosition.
I have tried changing the “interpolate” property of the rigidbody to Interpolate and extrapolate, but behaves the same.

My Fixed Timestep is 0.02 (default), if I get this value down, the stuttering stops, but I don’t want to use this method because I have to turn the value VERY low to work.

I am using Unity 2018.2

You can see the problem in this videos:

The videos are recorded at 60fps but my display is 144Hz and it makes it a lot more noticeable. The first example is a simple Unity camera and the second one is the Cinemachine freelook camera, this one is specially bad.

This is my code for the player movement:

void FixedUpdate()
    {
        rb.MovePosition(rb.position + this.transform.forward * inputMagnitude * speed * Time.fixedDeltaTime);
    }

    void Update()
    {
        // Checks if the player is grounded
        isGrounded = Physics.CheckSphere(groundChecker.position, groundDistance, groundLayerMask, QueryTriggerInteraction.Ignore);

        // Setup for movement
        if (isGrounded)
        {
            inputs = Vector3.zero;
            inputs.x = GamePad.GetAxis(CAxis.LX);
            inputs.z = GamePad.GetAxis(CAxis.LY);

            if (isCrouching)
            {
                inputs /= 2;
            }

            inputMagnitude = inputs.magnitude;

            animator.SetFloat("zSpeed", inputMagnitude);

            if (mainCamera.isActiveAndEnabled) inputs = mainCamera.transform.TransformDirection(inputs);

            inputs.y = 0;

            // Rotation changing the forward
            if (inputs != Vector3.zero)
            {
                this.transform.forward = inputs;
            }
        }
    }

Hi again! I have tried the following:

I have disabled the Auto Simulation in the project settings in Edit > Project Settings > Physics. I moved the part of the code that handles the character movement and rotation to Update and make a call to Physics.Simulate().

This solutions seems to get rid of the stuttering problem, but for some reason, the gravity seems to be doubled when i pass 0.02f to the Physics.Simulation function. (If I pass 0.01f it works fine)

Any ideas why is this happening?