Need help to solve problems with First Person Dungeon Crawler movement script

I have make an script to make a FPS Grid Based Movement with Vector3.MoveToWard & Quaternion.RotateTowards, I want to change it for Vector3.Lerp & Quaternion.Lerp but I do not know how to do it keeping movement time < cooldown.

this is the script:

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

public class Player : MonoBehaviour {

 Vector3 newPos;
 Quaternion newRot;
 Transform player;

 int gridSize = 2;
 int mSmooth = 6;
 int rSmooth = 360;

 bool hitF;
 bool hitB;
 bool waitW;
 bool waitT;

 void Start() {
     player = transform;
     newPos = transform.position;
     newRot = transform.rotation;

     hitF = false;
     hitB = false;
     waitW = false;
     waitT = false;
 }
 void Update() {
     if (Physics.Raycast (player.position, transform.forward, 1.5f)) { // check for forward move
         hitF = true;
     } else {
         hitF = false;
     }

     if (Physics.Raycast (player.position, -transform.forward, 1.5f)) { // check for backward move
         hitB = true;
     } else {
         hitB = false;
     }

     if (Input.GetKeyDown (KeyCode.W) && waitW == false && waitT == false && hitF == false) { // move forward
         waitW = true;
         StartCoroutine ("WaitingWalk");
         newPos = (transform.forward * gridSize) + transform.position;
     }

     if (Input.GetKeyDown (KeyCode.S) && waitW == false && waitT == false && hitB == false) { // move backward
         waitW = true;
         StartCoroutine ("WaitingWalk");
         newPos = (-transform.forward * gridSize) + transform.position;
     }

     if (Input.GetKeyDown (KeyCode.D) && waitT == false) { // turn right
         waitT = true;
         StartCoroutine ("WaitingTurn");
         newRot = newRot * Quaternion.Euler (0, 90, 0);
     }

     if (Input.GetKeyDown (KeyCode.A) && waitT == false) { // turn left
         waitT = true;
         StartCoroutine ("WaitingTurn");
         newRot = newRot * Quaternion.Euler (0, -90, 0);
     }

     transform.position = Vector3.MoveTowards (transform.position, newPos, Time.deltaTime * mSmooth);
     transform.rotation = Quaternion.RotateTowards (transform.rotation, newRot, Time.deltaTime * rSmooth);
 }

 IEnumerator WaitingWalk () { // walk cooldown
     yield return new WaitForSeconds (0.5f);
     waitW = false;
 }

 IEnumerator WaitingTurn () { // turn cooldown
     yield return new WaitForSeconds (0.3f);
     waitT = false;
 }

}