Vector3.Lerp is flinging my character all over the place!

I have a small game where you move a cube around some levels and I want to create an ice hazard that makes the player slide in a direction. I use the following code to do this,

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class iceController : MonoBehaviour {

 private IEnumerator coroutine;
 bool go = false;
 private Vector3 dest;


 private void Update()
 {
     if(go)
     {
         GameObject player = GameObject.Find("cube");
         CubeController cube = player.GetComponent<CubeController>();

        if(cube.lastmov == "up") //slide the player in the direction they are moving
         {
             dest = cube.parent.transform.position + (Vector3.left);
         }
         if (cube.lastmov == "down")
         {
             dest = cube.parent.transform.position + (Vector3.right);
         }
         if (cube.lastmov == "right")
         {
             dest = cube.parent.transform.position + (Vector3.forward);
         }
         if (cube.lastmov == "left")
         {
             dest = cube.parent.transform.position + (Vector3.back);
         }

         cube.parent.transform.position = Vector3.Lerp(cube.parent.transform.position, dest, .2f);
     }

 }

 private void OnTriggerEnter(Collider other)
 {
     GameObject player = GameObject.Find("cube");
     CubeController cube = player.GetComponent<CubeController>();
     go = true;
     cube.input = false; //stop the player from moving while sliding 
 }

 private void OnTriggerExit(Collider other)
 {
     GameObject player = GameObject.Find("cube");
     CubeController cube = player.GetComponent<CubeController>();
     go = false;
     cube.input = true;
 }

}

But for some reason this is giving me inconsictent results. sometimes it does exactly what I want it to do, but other times it will fling the cube across the map violently. Any ideas on why this is happening or how to fix it?

EDIT: It may not specifically have to do with Lerp. I attempted to do the same thing with transform.translate and ran into the same issue, so consider me baffled!