While that may be a valid issue...I have always noticed a clunk from just about any GM transmission in city driving, speeding up, letting off and letting it shift. My 89 bonne, 90 electra, 98 bonne, 93 bonne, hell, even my truck does that. Actually the truck does it audibly AND physically.
Not to try and muck up a technical post with non factual information, but I see it as normal. If you maintain your transmission, there is nothing to worry about, because if it is failing, theres nothing you can do anyways.