If you get more features, it means your 3760 changed to use new firmware.
3750 or 3760 won't get full function as 3790.
Word "3760" in inventory page won't changed because "word 3760" is in deep memory where we can't edit this number.(maybe other expert can do it )

.system is a hidden folder. You have to set your computer to access hidden files.

The step should be

5. Delete gupdate.gcd unter .System (How?)
6. Rename folders (Voice, Text, Keyboards) (Over USB?)
3. Make a hard reset.

1. Create your own gupdate.
2. Copy to SDCard \Garmin\gupdate.gcd

Then flash new firmware
9. Hope and pray!?

Nuvi boot up normally.

8. Rename the folders back to original. (Over USB?) --> Yes, via mass storage mode

7. Make another hard reset.