91 3spd auto trans no down shift to 1st

I have a 91 Caravan that has a 3 spd auto that has started not down shifting to 1st. Trans was totally rebuilt 50 K ago and serviced in between. It will manually downshift to1st and kickdown yto 1st Fluid is fine throttle pressure linkage is working I believe there was a valve body problem on this model Not sure? The trans was needlessly overhauled the 1st time due to a valve body problem as the trans did same thing the next day and $1200 dollars later. Thanks