ok correct name for 3D buildings map is gmap3d.img, this confused me.
the right path is .System hidden directory, you can check in your device.xlm

In 3790 you can put it also in sd/Map folder with its name gmap3d.img
CNE NTU map must be copied in your device along its own gmap3d.img NTU in .System folder.
gmap3d.img NT one wont show up with NTU map copied in .System or in sd-
But you can try to put your CNE NTU and gmap3d.img NT in Map folder renaming 3D map to CNENTUsamename3D.img probably it will show up-

example :

SD/Map/CNENTU.img
+
SD/Map/CNENTU3d.img

more infos here

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edit : correct path for *.JCV is : ( x:\Garmin\JCV )
in Garmin folder in a subfolder called JCV on the SD Card

in Garmin folder in sd in 37xx and new devices you can have just one gmapsupp.img, a second one wont show up