No matter what gears you have, you still have a 140hp engine coupled to a ~30% loss transmission from a minivan, in a car that weighs 2900lbs.

Anyone spinning tires with an automatic either has a turbo or is driving on ice covered by a large oil spill.

The specs for the final drive mod improvement were posted years ago, and my pics are still hosted.
http://forums.2gnt.com/dcboard.php?az=show_topic&forum=33&topic_id=2361&mesg_id=2361&listing_type=search

My results were: 0.57 seconds quicker 1/8 mile, 2mph faster.
This would probably translate to a 1+ second improvement and 4-5mph gain in a 1/4 mile. Hardly life-changing.