Hi @rlingeh
Definitely lots on this forum on the Asset Tracker (Search is your friend)
for example: Asset Tracker GPS -- Your experience with getting GPS fix
I managed to get the Asset Tracker working earlier this year.
Though to make getting a fix in any reasonable time I bought an active GPS antenna (like lots of others).
This seems to be almost essential for the GPS to work reliably and quickly.
The other thing I found useful, and seemed to help solve some of the problems you seem to be having too, was to switch to the TinyGPS library (made able to work in our Particle devices by @krvarma). Find details at TinyGPS and Spark Core.
These two changes made the Asset Tracker work for me, hope this helps.
NB: I am pretty sure I was able to get the NMEA sentences to be adjustable between the TinyGPS options of “GPRMC” and “GPGGA”.
This thread contains some good stuff on problems with the Adafruit library - and in particular on the issues around the NMEA sentence structure changeover: Default example for Asset Tracker GPS prints erratic NMEA sentences to serial
GM.