Problem solved. You'll never guess.
Tap on Photos. A photo will appear on the screen. Because Slideshow has been activated, the word "Slideshow" will appear in the upper, right hanbd portion of the screen. As long as that word is there, you will not be able to move photos manually because you are "in" Slideshow mode (it just isn't running).
To start SS, tap the word "Slideshow" and hit "Start Slideshow" in the dropdown menu. To get OUT of Slideshow mode, just tap the photo. When you do that, "Slideshow" will disappear from the upper right hand portion of the screen and, guess what - you can now move your photos manually.
So it isn't so much a matter of "deactivating" Slideshow as it is a matter of simply moving out of Slideshow mode.
If, in Slideshow mode, you attempt to move a photo, it SHOULD jump OUT of Slideshow mode the second you tap on (or touch) the photo. For some reason, my iPad was not doing that. Now it is. Don't ask me why.
Did we all learn something here? I know I did. Thanks for all your time and help.