Code not displaying/working DFRobot SIM808 shield data on Adafruit 1.69" ST7789 rounded screen

Question

I have been having trouble with the code below not display and possibly not working and or looping. Before making changes to my code I had a problem where the Serial monitor would print up to "longitude" and occasionally print the first number of this value, however, it would pause stop and the whole code would pause/not continue. I had printed data to the Serial Monitor constantly but was told that the problem could be that the serial monitor is full. With this, I have deleted most of the code for the serial monitor as it is not needed for my project. Now I cant tell at what stage my code is not working. The code for the screen is formatted this way as I have found it is the best way to reduce flickering, however I know there is a fast display library but was unable to implement it. Could it be battery issue? I am using a 9V battery to power all of the components. Any help would be much appreciated and the code is provided below.

#include <Adafruit_GFX.h> // Core graphics library
#include <Adafruit_ST7789.h> // Hardware-specific library for ST7789
#include <DFRobot_SIM808.h>
#include <SPI.h>
#include <Wire.h>
#define TFT_CS 10
#define TFT_RST 9 // Or set to -1 and connect to Arduino RESET pin
#define TFT_DC 8
#define date_x 20
#define date_y 17
#define time_x 20
#define time_y 35
#define v_x 17
#define v_y 70
float la;
float lo;
char DateGPS[10];
char TimeGPS[5];
String prevDate = "99/99/9999";
String Date = "00/00/0000";
String prevTime = "99:99";
String Time = "00:00";
String prevV = "999:99";
String V = "000:00";
Adafruit_ST7789 tft = Adafruit_ST7789(TFT_CS, TFT_DC, TFT_RST);
DFRobot_SIM808 sim808(&Serial);
void setup() 
{
 Serial.begin(9600);
 
 tft.init(240, 280);
 tft.fillScreen(ST77XX_BLACK);
 //******** Initialize sim808 module *************
 while(!sim808.init()) 
 { 
 delay(1000);
 Serial.print("Sim808 init error\r\n");
 }
 //************* Turn on the GPS power************
 if( sim808.attachGPS())
 ;
 else 
 ;
 
}
void loop() 
{
 //************** Get GPS data *******************
 if (sim808.getGPS()) 
 {
 sprintf(DateGPS, "%02d-%02d-%04d", sim808.GPSdata.day, sim808.GPSdata.month, sim808.GPSdata.year);
 Date = String(DateGPS);
 if(prevDate != Date)
 {
 deletePrevDate();
 printDate();
 }
 prevDate = Date;
 
 sprintf(TimeGPS, "%02d:%02d", sim808.GPSdata.hour, sim808.GPSdata.minute);
 Time = String(TimeGPS);
 if(prevTime != Time)
 {
 deletePrevTime();
 printTime();
 }
 prevTime = Time;
 
 Serial.println(sim808.GPSdata.lat, 6);
 
 Serial.println(sim808.GPSdata.lon, 6);
 
 V = String(sim808.GPSdata.speed_kph);
 if(prevV != V)
 {
 deletePrevV();
 printV();
 }
 prevV = V;
 //************* Turn off the GPS power ************
 sim808.detachGPS();
 }
}
void deletePrevDate()
{
 tft.setCursor(date_x, date_y);
 tft.setTextSize(2);
 tft.setTextColor(ST77XX_BLACK);
 tft.println(prevDate);
 return;
}
void printDate()
{
 tft.setCursor(date_x, date_y);
 tft.setTextSize(2);
 tft.setTextColor(ST77XX_WHITE);
 tft.println(Date);
 return;
}
void deletePrevTime()
{
 tft.setCursor(time_x, time_y);
 tft.setTextSize(2);
 tft.setTextColor(ST77XX_BLACK);
 tft.println(prevTime);
 return;
}
void printTime()
{
 tft.setCursor(time_x, time_y);
 tft.setTextSize(2);
 tft.setTextColor(ST77XX_WHITE);
 tft.println(Time);
 return;
}
void deletePrevV()
{
 tft.setCursor(v_x, v_y);
 tft.setTextSize(6);
 tft.setTextColor(ST77XX_BLACK);
 tft.println(prevV);
 return;
}
void printV()
{
 tft.setCursor(v_x, v_y);
 tft.setTextSize(6);
 tft.setTextColor(ST77XX_WHITE);
 tft.println(V);
 return;
}

• jsotola: serial monitor is full is nonsense ... you can test that with a sketch that sends a lot of data
• jsotola: please roll back your code to the previous version with lots of serial.print ... copy the content of the serial monitor and paste it into your question ... format it as code for readability ... please, no screenshots of text