91 buick regal 3.8 trans problem !!?

car has 63,000 miles and trans seems to go in to a neutral state for a few seconds when coming to a complete stop and trying to accelerate again ! I have changed the fluid and filter recently and ck'd the level, its fine. the fluid was alittle dis-colored but not burnt smelling.after changing the fluid, the car drives real good and shifts when it is suppose too. MY question is what could make this hesitation when coming to a stop, whether it is a fast or slow stop.this happens in over/drive or regular drive gear.the car has never been dogged or abused !