Hi
I get nuvi37xx_regionfileonly__250.gcd from garmin server. Use RGNTool and make a .rgn file.
Use hex editor and change nuvi 37xx to nuvi 3790, save .rgn and use updater.exe in pre-boot.

Now in about it said nuvi 3790 and in the boot text show nuvi 3790

Now I'm doing a webupdate to see if it's works.