Stutter problem, no physics

Can't deal with a stutter issue. Moving object in Update, using Time.deltaTime. No physics.

Object moves from point to point.
Without rotation it moves smooth, but when I add rotation logic I can see the motion stutter. I've tried different ways to solve this - tied FixedUpdate, smoothDeltaTime etc etc - nothing helped (

Maybe some one can give an advice - I am totally frustrated and can't continue developing my game.

    public void Update()  {
         var nextStep = GetNextStepData(currentGoalPoint, transform.position,
             (transform.rotation.eulerAngles.z + 90) * Mathf.Deg2Rad);
 
         CurrentSpeed = nextStep.Speed;
         transform.position = nextStep.Position;
         transform.rotation = Quaternion.AngleAxis(nextStep.Rotation * Mathf.Rad2Deg - 90, Vector3.forward);
     }


  protected NextStepData GetNextStepData(GameObject goalPoint, Vector3 currentPointPosition,
         float currentPointRotationRadians)
     {
         var timeCoeff = Time.deltaTime * 15f;
 
         var deltaY = goalPoint.transform.localPosition.y - currentPointPosition.y;
         var deltaX = goalPoint.transform.localPosition.x - currentPointPosition.x;
  
         var goalRotation = Math.Atan2(deltaY, deltaX);
 
         var rotationDelta = goalRotation - currentPointRotationRadians;
  
         while (rotationDelta > Math.PI)
         {
             rotationDelta -= Math.PI * 2;
         }
         while (rotationDelta < -Math.PI)
         {
             rotationDelta += Math.PI * 2;
         }
 
         currentPointRotationRadians = (float) (currentPointRotationRadians + rotationDelta * TurnCoeff * timeCoeff);
 
         var dirX = (float) Math.Cos(currentPointRotationRadians);
         var dirY = (float) Math.Sin(currentPointRotationRadians);
 
         return new NextStepData
         {
             Position =
                 new Vector3(currentPointPosition.x + dirX*timeCoeff, currentPointPosition.y + dirY * timeCoeff,
                     currentPointPosition.z),
             Rotation = currentPointRotationRadians,
          };
     }