30,000 mile trans oil changes are good, maybe a little more frequent after 150k if it is the original trans at that stage. I personally don't like "flushing" machines, have seen them dislodge debris causing problems rather than helping matters. Dropping the trans pan and changing the filter were applicable is best.
In most cases, if you change your transmission fluid every 30K then you should not need a transmission fluid flush. However, if the fluid were to become discolored or brunt smelling then a flush would be in order.