Look at script wrong at high speeds

I've tried numbers of look at scripts, but whenever they get to a high speed, they are always a little offset. It's hard to explain, so I made 2 .gifs so you can see.

The enemy ship follows you and turns to face you. when it is hit by a projectile, it stops. Once the linecast coming off the enemy hits the player, it resumes looking at the player.

http://i.imgur.com/hTxAJpG.gif

But if the enemy moves at a high speed, it gets offset. I've noticed this problem allot in unity, but in this game I can't let it slide as easily.

http://i.imgur.com/bjz8kKg.gif

Here are some scripts I have used:

          var newRotation = Quaternion.LookRotation(transform.position - target.position, Vector3.back);
  
          newRotation.x = 0.0f;
  
          newRotation.y = 0.0f;
  
          transform.rotation = Quaternion.Slerp(transform.rotation, newRotation, Time.deltaTime * rotatespeed);

(currently using that one ^^^)

      var dir = transform.position - target.position;
      var angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
      var newRotation = Quaternion.AngleAxis(angle, Vector3.forward);
      transform.rotation = Quaternion.Slerp(transform.rotation, newRotation, Time.deltaTime * rotatespeed);

,

     rigidbody2D.transform.eulerAngles = new Vector3(0,0,Mathf.Atan2((TARGETTRANSFORM.position.y - transform.position.y), (TARGETTRANSFORM.position.x - transform.position.x))*Mathf.Rad2Deg - 90);

I tried all these scripts and noticed no difference. I have tried using 3D and 2D colliders (currently using 2D) and have found no difference. I tried using the Update, LateUpdate, and FixedUpdate. While fixed update is the smoothest, it doesn't fix the problem.

If there is some way to refresh the looking script, or get it to be more accurate (preferably with an adjustable speed), that would be fantastic.