Garmin POI Loader (v 2.4.0 or higher) has an option to uninstall all custom POI's from your GPS.
Using this feature doesn't remove the regular built-in POIs that were pre-installed on your GPS.
However, for units that come preloaded with the the NTTS trucking database, it appears that POI Loader DOES delete this information. Like custom POI's, it's stored in a GPI file.
== USE POI LOADER TO REMOVE CUSTOM POIs ==
Connect your GPS to the computer and run POI Loader.
After finding and selecting your GPS device, select the option to "Remove all previously installed custom POI's from your device"
POI Loader will warn that you'll need to run it again if you want to reinstall POI files.
== CONFIRM THAT THEY'RE GONE ==
There are unusual situations where POI Loader may not remove some custom POI files.
Start the GPS and check to see if all the custom POIs are, in fact, gone from the device. If any are still loaded, you'll find them at one of these two locations (depending on the model):
Where to? > Categories > Other / Custom POIs
Where to? > Extras > Custom POIs
== CUSTOM POIs THAT DIDN'T GO AWAY ==
If the GPS still has custom POIs, it's likely that there's an extra .GPI file somewhere on the device. This can happen if you've manually moved GPI files on the GPS or if you've mistakenly saved a backup onto the GPS instead of your computer.
On Apple computers, you may need to "empty the trash" while the GPS is still connected in order to get the POI files to go away. Even if the trash already appears to be empty, this step is sometimes required.