aster94:
I am using a neo-6mtookI bought on aliexpress for 6euros. A few peoplesaidtold me that it could be a fake, what do you think about [that]?
Maybe.
Have you ever tried to upgrade the firmware of a ublox gps?
No.
Be sure you are level-shifting 5V Arduino signals down to 3.3V for the GPS RX pin. A resistor divider will work for that.