Hey, I actually figured this out.
Notsonormal, maybe this will work for you?
In the Forum Manager, within each individual forum's settings, I happened across an option called "Index New Posts in Search Engine." Apparently the default is off. By turning it on, suddenly posts were searchable. Duh! to me, right?

Now I have to go into each forum and make this switch.
I'd never spotted this option before. (In my meager defense, vb3 is still new to me.) But geeze, does it strike anyone else as kinda annoying and bass-ackwards that by default, forums are
not indexed? Not to mention only putting this option within the forum manager, rather than the vbulletin options area as a global option (that's able to be set individually as well)?
Weird. Anyway,
Notsonormal, check each forum's settings and see if this option is available to you. Good luck.