On further investigation, I found a website that has some tips on what
to look for. They said to get the dishwasher running, then stop it,
put a glass in the upper tray, restart and run for 30 secs. If the
glass isn't full, either it doesn't have enough water, or the pump is
kaput. Well, in 30 secs, I get maybe an inch, in a min and a half I
get about a half glass. It has enough water, I even tried adding some
more so it was almost overflowing. It's pretty clear now that
inadequate water flow is the problem.

So, unless anyone else has any good ideas, I think it's time to start
tearing it apart. Good news is there appears to be an impeller kit for
$22 available.