So, after several trials, it's time to share my experience with rolling back the firmware.

My Nüvi is 2597, software version 7.6 and GPS firmware: 5.08.11, all updated with Garmin Express.

I wanted to do the rolling back so I could install, through Mapsource, a topo map into my nuvi, or other kind of maps.

I tried the tutorial from #catymag "How to reverse back your Garmin unit to a previous FW version", but I was not successful in any of the parts.

first, the part:
"Run WebUpdater without disconnecting the nuvi as rebooting the device will re-generate the GarminDevice.xml file restoring it's correct values. Upon checking for a new version (and finding one since you've fooled it into thinking that an earlier version is on the unit), there will be a link to an "additional info" webpage. Click on the link. "
second:
(...)connect the gps to the PC's USB port and allow it to be detected. Now drag the downloaded file to your WebUpdater icon. "
" Also did not work

Then, thirdly, I tried a different approach, from #dasilvarsa: "Another method is to rename nuvi24x5and25x5_GCDFile__780.gcd [example] to gupdate.gcd and
then copy the file to the hidden /.System folder. After Nuvi is switched On it will flash."

Mu nuvi always stayed with the same version, 7.60, no flashing.

By the way, the only link that works, to download files with previous firmwares, is
Code:
Please Login or Register to see the links