Start by performing a FAT32 'Full' (not 'Quick') format of your unit. You'll need to connect it, so when Home appears, just close it out with the "X" for now. We'll get back to it later.
Once the format is complete, disconnect your XL with a proper Windows logical USB disconnect (use the icon in the systray) and reconnect it again. This time, when Home appears, it's going to suggest some firmware to you since it won't find any on the unit.
Accept whatever firmware is offered by Home and get it installed on your unit.
Perform the proper USB disconnect using Home (I use the little down arrow in the lower right of the Home screen), physically disconnect your unit and connect it again.
IF Home then offers yet more firmware updates, install them until it ceases to offer any firmware updates.
At this time, you can minimize (not close) Home to get it out of your way, and go to your PC backup copy of the US/Canada/Mexico or North_America (or whatever it was called on your 350) map folder. Copy that entire folder over in to the root of your XL.
Bring Home back to the fore and again, do a proper USB disconnect with Home.
Disconnect your XL from your PC and shut it off. Restart and tell us how you're doing.