The uneven wear on the driver side probably is a result of a bad wheel
bearing which I replaced about two weeks ago. It was very noisy driving above
45mph. I think the wheel alignment is fine, because the van does not move to
one side even I release the steering wheel, and very firm at high speed
(65mph).
Now I just found both of the lower and upper ball joint boots on the
passenger side have been broken, but the wheel still very firm with no play
when I shake the wheel. This will be another project, another challenge in
the near future.

Thanks again for all the excellent suggestion.

Albert