Originally Posted by bmw160
I want to be quicker off the line and be able to beat them across the light
Unfortunately you are starting with a hard sixxer to mod. The best thing you can do first and for most to get the most out of you sixxer is a spit-port swap from a 99-04 3.8 coupled with a windstar intake from a 94-98 windstar. This will not be the cheapest but will net you in the range on 30-50 rwhp and will respond better to other mods because of the increase air flow.
That being said, if your just looking for an increase in acceleration, gears would be your best bet. Its somewhat pricey (probably in the $500-800 range with labor) but will give you the best results vs just about anything you can do and will get you to your current goal. My recommendation would be 4.10s minimum. There's general ideas for gears out there that alot of people go by that say 3.73s for manual and 4.10s for autos, but IMO, on the 3.8, 4.10s would be the lowest I would go. I would even go as far as 4.30s or 4.56s.
But based on your goals and I assume this is a DD, I think 4.10s would be perfect for what your after.
Also look around v6power.net and 3.8mustang.com. Both are great resources for this motor.