Unfortunately as we eliminate each possible soft problem the more likely a hard-bricking due to physical flash damage becomes.

Not done yet however, there's still some tricks to try.

I doubt it can read directly from a microSD card because it's stuck on the logo, but because preboot is working we should be able to get it reading from and writing to a card using a modified boot.bin as RGN. I'm sure you you know how to use a Hex Editor so follow the guide in [Only registered and activated users can see links. ] to make 110601000630.rgn and then try a backup of its nonvol region 41. Make the SD flash kit normally following [Only registered and activated users can see links. ] but don't have Ldr.bin in the 1106 folder with Update.txt file. This is the command:
Code:
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With the card inserted, load the RGN to Updater.exe then connect the nuvi in preboot. Run Updater normally. Report result.

If unsure of how to do it, ask and i'll make the kit for you when i have time.

If it dumps region 41 ok then we can also erase 41 just in case it's got poisoned data in it preventing the boot or the completion of a successful flash. Depending on results we can maybe also do flashing of cure fw using the same method after also dumping the main firmware region 14 to check for problems there. But let's take it slow and step-by-step.