Bad shocks could lead to your condition, but with that many miles,
probably not. I can see the fronts being caused by misalignment but not
the rears. If the rears are cupped it's either the tire pressure being
too low, an out of balance condition or the tires themselves. I would
think if they are out of balance enough to give you your wear pattern,
you should certainly feel it while driving so this theory is a stretch.
Good luck.