I came across this topic: Is there a debugged asset tracker GPS library yet? in which someone mentioned digitalWrite() coupled with pinMode() should correctly disable the GPS module before System.sleep.
So if I understand correctly, in Reset_state I should simply use digitalWrite() to set D6 to HIGH, and then set D6 to LOW in the same fashion in GPS_Wait_state to turn on the GPS for signal collection? And leave the pinMode() to Output throughout all of the code?