Performance Issue on Update

I'm having trouble figuring this out. I'm trying to slow the speed of an object depending on another script [the score]. Problem is that performance is really bad, and doing a Coroutine isn't very practical since checking the score every X amount of time - might actually not work all the time.. I.E. What's the chance of hitting the score on the 5th second that the Coroutine is ran?

Here is my script:

 public class MovePlank : MonoBehaviour
 {
     public float plankMover = -2.0f;
     ScoreTracker checkScore;
 
     public float amplitudeX = 10.0f;
     public float amplitudeY = 5.0f;
     public float omegaX = 1.0f;
     public float omegaY = 5.0f;
     float index;
     float checkScoreTime = 5.0f;
     bool checkLevelOne = false;
 
 
     // Use this for initialization
     void Start ()
     {
         checkScore = GetComponent<ScoreTracker>();
     }
     
     // Update is called once per frame
     void Update ()
     {
         StartCoroutine(WaitToCheckScore(checkScoreTime));
 
         transform.Translate(plankMover * Time.deltaTime, 0f, 0f);
 
         if (checkLevelOne)
         {
             /* index += Time.deltaTime / plankMover; //this changes the X speed as it technically slows down time. Increase paintSpeed to slow it down further.
              float x = amplitudeX * Mathf.Cos(omegaX * index); //amplitude X is the X value as where it'll generate while omegaX shouldn't really be touched. 
              float y = amplitudeY * Mathf.Sin(omegaY * index); // amplitude Y is the Y value as where it'll generate and omegaY is how many times it goes up and down.
              transform.localPosition = new Vector3(x, y, 0); */
              transform.Translate(plankMover / 2 * Time.deltaTime, 0f, 0f);
         }
     }
 
     IEnumerator WaitToCheckScore (float checkScoreTime)
     {
         yield return new WaitForSeconds(checkScoreTime);
         if (checkScore.levelOne)
         {
             checkLevelOne = true;
         }
     }
 }

Suggestions?