1989 Dodge caravan cupping tire tread

What would be the cause of cupping of the rear passenger side tire?By time I got to it the tire was toast, my wife is up and gone at 5 am and back at
dark.This poor mini-van never stops.141,000 miles.So anyway I replaced the rear shocks and replaced the tire.Any ideas as to other ways of clearing up this problem? Thank you all.
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You mention nothing about balancing the tires? This needs to be done.
Glenn Beasley Chrysler Tech
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