Thanks for the reply!
Something got upset and it all stopped working. I disconnected the batteries. For four hours I tried every possible option - reading or test flashing with the ignition key in various positions. I finally got to a place where the Scan tool wouldn't read anything and the flash tests just failed.
Disconnected the batteries and let it set. Reconnected and all seemed fine.
So, tried one last time. This time I de-selected the option for a high speed link. Now a flash with the current tune in Test mode finally worked!
So, I think I finally learned enough to be dangerous.
I have a tune file to load. It's for use with a DSP5. Do I do a flash, or a complete program with OS?
Truck is 2004.5 LLY that I bought new - so I know it has never been reprogrammed by anyone but my dealer.