Updating a UI Text at a set rate using numbers from an array

Hello! So I'm writing a script that will display the altitude of my gameobject as it travels. I'm getting its altitude from a text file that I've put into an array. Here's my code so far:

 using UnityEngine;
 using UnityEngine.UI;
 using System.Text;
 using System.IO;
 using System.Collections;
 using System;
 
 public class PlayerController: MonoBehaviour {
 
 
     private Vector3 position;
     private double[] nums;
     private double altDisplay;
     public Text altText;        

     void Start()
     {
         //Import text file and read all.
         string text = System.IO.File.ReadAllText("File.txt");
         if (text != null) 
         {
             //Split the string of text into an array containing each number in the file.
             string[] strings = text.Split (new[] { " ", "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
 
             //Convert each string number to a double.
             nums = new double[strings.Length];
             for (int i = 0; i < strings.Length; i++) 
             {
                 nums [i] = Convert.ToDouble (strings [i]);
             }
                 
         }
     }
 
     void FixedUpdate()
     {
 
         //Common variables
         int Entries = 6992;
         float speed = 1.0f;
 
         //Determine the Y altitude
         float yMeters;
 
         for (int i = 3; i < Entries; i += 7) 
         {
             yMeters = Convert.ToSingle(nums [i + 7] - nums [i]);
             transform.position += transform.up * yMeters * Time.deltaTime * speed;
         }
 
         for (int i = 3; i < 6999; i += 7) 
         {
             altText.text = (nums[i]).ToString () + "m "; 
         }
     }
 }

The reason my for loop starts at 3 and increments by 7 is because my text file has 1000 lines that look like this

x1 x2 x3 x4 x5 x6 x7

and the altitude that I need is the x4 number of each line. My problem is that when I click play, the only altitude that is displayed is the very last one. I understand that the for loop is probably running through each one very quickly, so I guess my question is: How do I get the text to update at the same rate that my gameobject is updating?