same things happen to me ..dips from 5th to 4th (only from 5th to 4th) and around 2500rpms as if the car could pass that rpm limit and needed to dip to get some acceleration then comes back to 5th when idle... sometimes with a loud bannng that shakes the car .
got new tranny so thats not it
the guy with an answer to this will b my hero

__________________
03 4.6is