My sincere thanks to those trying to help me. I've found the problem and feel extraordinarily stupid. In looking at screenshots in a tutorial, I realized the box that pops up for the controls for the graduated filter was collapsed on my screen. Once I clicked the arrow and got the proper controls, it works like it should. It's been a while since I felt this dumb!! But I guess that's why they call it the Beginner's forum, eh?
Thanks again!