Where you end up with Tools/Custom Probes is the edit dialog. This is where you create, import, export, and modify the custom probes. You do not select them from there. You select them from the channel options button probe drop down.
Since you are new at this, perhaps you would benefit from this little movie:http://www.autonerdz.com/flash/ps6intro.html
One of the things in the movie shows you where to select the custom probes.
With your 3223, you will want to turn up the requested sample rate to the max and leave it there. The automotive menu selections dummy that way down so you cannot then put more time on the screen without signal degradation.
(The Picotologist) http://www.autonerdz.com
THE PicoScope Automotive Authority
In North America