As there are more modern options to reliably transmit data to a ground station, I decided to switch from Talky to a HopeRF RFM98PW Lora module. This module is max 1 watt and can be easily implemented using the Arduino Radiohead library.
In addition, the trusted Atmega 328P has been replaced by the faster SAMD21G MCU with more memory and an embedded USB port/
Barometric pressure is measured using a MS5611 unit
Finally, the quectel L96 GPS unit has been replaced by a Ublox neo-9. This unit has better dynamic properties and allows for a maximum altitude of 80kms.
Deelmanl 
Really an impressive work. I hope you have the opportunity to test the neo-9 to its boundary.
Best Regards/
Göran Bergman