Touch movement - freedrag jittery with tilt from spaceshooter

ok guys, ive got my touch controls working at the moment, but unfortunately its a little bit jittery, i find if the user moves really slowly its really responsive, however if you move quickly around the screen, its much slower to move around, i think maybe the normalize is causing it but i couldnt find a better solution(im new to coding)

speed is a float variable set in my GameController

     `void FixedUpdate ()
 {
     float moveHorizontal;
     float moveVertical;

     moveHorizontal = Input.GetAxis ("Horizontal");
     moveVertical = Input.GetAxis ("Vertical");

     Vector3 movement = new Vector3 (moveHorizontal,moveVertical, 0.0f);
     rigidbody.velocity = movement * speed;


     gameControllerScript = gameControllerObj.GetComponent<GameController>();
     if(!gameControllerScript.restart)
     {
         if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Moved) {
             Vector2 touchDeltaPosition = Input.GetTouch(0).deltaPosition;
             Vector3 movementDelta;
             movementDelta = new Vector3(touchDeltaPosition.normalized.x, touchDeltaPosition.normalized.y, 0);
             rigidbody.velocity = movementDelta * speed;

             //transform.Translate(touchDeltaPosition.x/30, touchDeltaPosition.y/30, 0);
             //Debug.Log ("you jus DRAG dem one");
         }

         rigidbody.position = new Vector3 
         (
             Mathf.Clamp (rigidbody.position.x, boundary.xMin, boundary.xMax),  
             Mathf.Clamp (rigidbody.position.y, boundary.yMin, boundary.yMax),
             0.0f
             );
     }
     if(gameControllerScript.restart)
     {
         Debug.Log("Restart TRUE");
         if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Began)
         {
             transform.position = gameControllerScript.playerSpawn;
             gameControllerScript.restart = false;
             gameControllerScript.spawnMultiplier = 0;
 
         }
     }
     
     rigidbody.rotation = Quaternion.Euler (rigidbody.velocity.y * tilt , rigidbody.velocity.x * -tilt, 0.0f);
 }