Wanted to give this idea to Kunix. Hope he reads my comment. I read he made it on the firmware of other nuvis I think. And could be a solution to similar problems where there seems to be a partial damage of the the memory of the nuvi - the nuvi can be turned on, boot loader can be loaded, even the system firmware! but there is problem in the FS (0x48). Kunix can you prepare a tool where the system firmware does not read 0x48 but an SD card insted? Or this is not possible? Just nuvi to ignore reading from this part of the memory?

BTW what is on 0x66? Why are you deleting it?