Normal Walker Script Rotating Player Orientation Incorrectly?

I found a script recently that allows you to walk on an object and rotate based on the normals below the object. The problem is that the player y rotation snaps back to 0 whenever the rotation of the player is modified. This is a problem as I am making a first person game where you navigate the inside of a tube. Also how would I make the transition smoother when the player rotation changes. I know I would need to add a slerp or lerp of some sort but I am a noob and am not familiar with quaternions.

using UnityEngine; using System.Collections;

public class NormalWalker : MonoBehaviour { //this game object's Transform
private Transform goTransform;

 //the speed to move the game object  
 private float speed = 6.0f;
 //the gravity  
 private float gravity = 50.0f;
 
 //the direction to move the character  
 private Vector3 moveDirection = Vector3.zero;
 //the attached character controller  
 private CharacterController cController;
 
 //a ray to be cast  
 private Ray ray;
 //A class that stores ray collision info  
 private RaycastHit hit;
 
 //a class to store the previous normal value  
 private Vector3 oldNormal;
 //the threshold, to discard some of the normal value variations  
 public float threshold = 0.009f;
 
 // Use this for initialization  
 void Start()
 {
     //get this game object's Transform  
     goTransform = this.GetComponent<Transform>();
     //get the attached CharacterController component  
     cController = GetComponent<CharacterController>();
 }
 
 // Update is called once per frame  
 void Update()
 {
     //cast a ray from the current game object position downward, relative to the current game object orientation  
     ray = new Ray(goTransform.position, -goTransform.up);
 
     //if the ray has hit something  
     if (Physics.Raycast(ray.origin, ray.direction, out hit, 5))//cast the ray 5 units at the specified direction    
     {
         //if the current goTransform.up.y value has passed the threshold test  
         if (oldNormal.y >= goTransform.up.y + threshold || oldNormal.y <= goTransform.up.y - threshold)
         {
             //set the up vector to match the normal of the ray's collision  
             goTransform.up = hit.normal;
         }
         //store the current hit.normal inside the oldNormal  
         oldNormal = hit.normal;
     }
 
    
 
 }

}