It seems you were right about the power relay, though it wasn't the relay itself. Finally got around to checking things this afternoon.
I had sweetie start it up, then tapped the relay assembly and various connectors with a screwdriver handle. Nothing happened.
So I unclipped the relay assembly cover, and as I slid the assembly out of the cover, the engine died. I told her to leave the key on.
The red wire going to the power relay was horribly loose.
I could touch it and the relay would click on and off. I pulled the relay and popped its cover off to make sure, but everything looked pristine inside (coil connections, contacts, etc.). So I buffed the contacts with a piece of card stock for good measure and put it back together.
I then removed the other relays and diode (which tested ok), and popped off the yellow piece that allows access to the wire connectors. Removed the red wire (and yellow, since it also looked a bit wide), crimped the female spade connectors for a snug fit on the relay, and put everything back together.
It idled ok for about 1/2 hr, and ran just fine on a test drive.
I really appreciate the help guys. Best wishes.