Arduino UNO + SIM800L (SMS) + NEO M6 (GPS) = Serial issues

Hardware Arduino GSM Shield
1

Hi everyone,

I'm trying to send my GPS location by SMS, using an Arduino Uno, with SIM800L at Serial (7,8) and NEO 6M at Serial (10,11).

The code is below:

#include <Sim800l.h>
#include <SoftwareSerial.h>
#include <TinyGPS.h>

SoftwareSerial GPS(5, 6); // RX, TX (GPS)
SoftwareSerial SMS(7, 8); // RX, TX (SMS)
TinyGPS gps1;
Sim800l Sim800l;

char latBuffer[20];
char longBuffer[20];
char fullBuffer[100];

void setup()
{
  Sim800l.begin();
  GPS.begin(9600);
  delay(1000);
  SMS.begin(9600);
  Serial.begin(9600);

  Serial.println("Waiting...");
  GPS.listen();
  delay(1000);
}

void loop()
{
  bool rec = false;
  bool rec2 = false;

  while (GPS.available() > 0)
  {
    rec = gps1.encode(GPS.read());
    break;
  }

  if (rec)
  {
    Serial.println("----------------------------------------");

    //Latitude e Longitude
    float latitude, longitude;
    unsigned long age;
    gps1.f_get_position(&latitude, &longitude, &age);
    float lat = latitude;
    float lon = longitude;

    if (latitude != TinyGPS::GPS_INVALID_F_ANGLE)
    {

      Serial.print("Latitude: ");
      Serial.println(lat);
    }

    if (longitude != TinyGPS::GPS_INVALID_F_ANGLE)
    {
      Serial.print("Longitude: ");
      Serial.println(lon);
    }

    dtostrf(lat, 0, 4, latBuffer);
    dtostrf(lon, 0, 4, longBuffer);
    sprintf_P(fullBuffer, PSTR("Lat: %s; Lon: %s"), latBuffer, longBuffer);
    Serial.println(fullBuffer); //show in Serial

    GPS.end();
    delay(1000);
    SMS.listen();
    delay(100);

    while (SMS.available() > 0)
    {
      Sim800l.sendSms("+XXXXXXXXXX", fullBuffer);
      delay(1000);
      GPS.begin(9600);
      delay(1000);
      GPS.listen();
      delay(1000);
    }
  }
}

What I get on Serial:

Waiting...
----------------------------------------
Latitude: -21.98
Longitude: -47.88
Lat: -21.9841; Lon: -47.8832

And it stops.

I tried everything I've read in web, like ".listen()" commands, "delay()", but, it seems that SMS Serial is never available. I edited the SIM800L library to set pins 6 and 7 for RX and TX. It worked when it's alone, but when I attach the GPS shield, it stops.

Did someone have the same problem?

Thank you!