just updated my nuvi 360 after a big struggle. posting here it might help some one.
nuvi 360 don't recognize map bigger then 2 gb even in SD card. I downloaded the us and canada latest map. it was bigger then 2 GB. after that i installed a
GMapTool app. with the help of that map i did split map. App split that map in 50-60 files. then i gone through many file that i don't need it. like Alaska, Mexico, Carolina, Kentucky, Pennsylvania and may more until its size gone close to 1.5 GB. Then i joint those files with GMapTool Map app. and created a smaller map. and swamped that map with my older map in the GPS HD. change that map name to ........gmapprom ----Disk Image File. thats it you are done.
you can choose which file to delete. for me i live in BC Canada so basically i need BC and i kept mostly Canada map and some nearby American states.
so keep the map files less then 1.5 GB and you are good. Have Fun.

@adam13 This is a good way to have a map just for print only! Unfortunately the map that you created will not support anymore any routing, meaning it should not work well. The only way to create a smaller map is to uploaded in Mapsource then choose the areas that you like and install them on the device or SD. If the maps are locked you have to unlocked them.

i am using that GPS for about few weeks now and its works absolutely fine, without a single problem. no delays works absolutely fine like normal GPS. just an example some of there area (files), i don't need in my map so i delete those....

Map length s-f CP prio PID FID name
I11A4A0F NT 24520150 1 1252 30 S 1 3326 WESTERN ALASKA
I11A49CE NT 16926708 1 1252 30 S 1 3326 EASTERN ALASKA
I11A49C0 NT 190694 1 1252 30 S 1 3326 CAYMAN ISLANDS
I11A49BF NT 188500 1 1252 30 S 1 3326 GRAND BAHAMA
I11A49C2 NT 217719 1 1252 30 S 1 3326 NEW PROVIDENCE
I11A49A8 NT 4618856 1 1252 30 S 1 3326 NORTHWEST TERRITORIES

I guess you may be right, but the way i did its worked for me and its working fine.