Fozzy.1990

i have a 97 integra GS, with a b20B automatic. When i bought the car. it shifted hard in low RPM's, and when going from park to reverse or drive. changed the transmission, ran great at first, then slowly started hard shifting again, i cant figure it out,ive done a tranny flush. i did some research, i was told it can be the transmission control module.
where is that located?
are they engine/transmission specific?
could this be what is wrong or any other ideas?
thanks in advance