Thanks for the replies.
I don't know if a compression test was done.  They hooked it
up to the "computer" and said there were no codes of any kind.  I don't know
if a compression test was done or if it was checked for vaccum leaks. Those
would be a good questions to ask.  How does one check for vacuum leaks?  The
problem occurs at idle as well as highway speeds.

I changed out the spark plugs, plug wires, air filter, fuel filter, and
changed the oil to rule out all (or at least some of) the simple stuff.
There was no change in symptoms.  I've googled myself silly on this problem
and didn't find anything that really applies to my situation.  That's why I
took it to Ford dealership in the hopes they might be able to figure it out.
What took me $85 to find out is they want to do what amounts to exploratory
surgery by taking the valve covers off.  This means new valve cover and
intake manifold gaskets at dealer prices plus another labor charge which
will be somewhere north of $200.  I'll have to look into a second opinion,
although it's hard to find repair shops that are interested in doing more
than brakes, plugs, oil changes, etc. (ie the routine stuff I can do
myself.)