Actually the firmware has not changed.
Only the Version Number has changed because it was edited.
3490 is using
GPS Firmware 2.28.12
Bluetooth Firmware 3.0.11 p32
PMIC version 119
Tsc Version 1.08
I actually think that when 3790 is flashed with 3490 firmware it finds the hardware is different and it does not flash the GPS chip at all.
If the 3490 actually has a better, more accurate GPS Chip then it's impossible to Make a converted unit behave like a 3490 because the chip is actually different.
We don't have concrete evidence of this fact.
Does the 3490 have a different GPS Chip ?