As usual, the experts here nailed this diagnosis. I found out for sure by taking it to the Apple Store for diagnosis and treatment. All is now well except my early 2008 Mac Pro is getting long in the tooth. It can't do some things provided by Yosemite, but those things aren't really a necessity for my operation anyway. I am, however, starting to look to the future. I now have 6 GB of RAM instead of 8. Frankly, I don't notice much of a difference.
Edited by JoBoy (11/26/14 11:26 AM)
Mac Pro dual Quad-Core Intel Xeons Early 2008; 16GB RAM; MacOS X 10.11.6, iOS 9.3.5