as i understand it the filter is internal and not a maintainance type changeable thing....only when 'major' work is being done would it be changed....i think...
when u had your fluid changed how was it done? if done by a power flush (machine instead of by hand) theres been a few of us on this site that have suffered atx problems after having the tranny serviced....my atx died 3 weeks after the flush
unfortunately the ford remanufacture atx the mis-dealer put in doesn't inspire much more confidence