I highly recommend 4.10s or 4.30's for an automatic, whether daily driver or not. I have 4.30's in my 01 auto GT which I drive normally and I really didn't see any loss in mpg with the gear swap. I use OEM 4.30 gears and I got them from Randy Stinchcomb. He is a Ford parts dealer but is out of his office until the 8th of this month I believe.
You can contact him here though:
http://forums.modulardepot.com/forumdisplay.php?s=&forumid=21 I highly recommend you talk to him first before ordering gears. He will help you with all the parts you need.
A lot of guys also buy Ford Racing gears at placings like
www.stangstore.com and
www.mustangtuning.com
As Stanlou said above, I would get them installed by someone who knows what they're doing. Changing gears insn't like changing spark plugs. This is actually something that is difficult and requires precision. For the gear install, you will also need 2qts. of rear diff. fluid and a 4oz. bottle of friction modifier. Randy can get you this stuff as well so mention it to him when you contact him.
Since you have an automatic, you will need something to correct your speedometer and your shift points with the new gears. I highly recommend Superchips Tuning. They can burn you a custom chip that you can plug into your computer and it should work fine when correcting the speedometer and shift points. You could always go the cheap route and buy a speedo gear to correct the speedo but I don't recommend that as it is inaccurate by nearly 10mph and will not do anything to correct your shift points. For an automatic, your only choices to correct the shifts and speedometer in one process is either buy a hand held programmer that will let you flash the computer, a chip, or dyno tune. Out of the three, a dyno tune is best but will be more difficult as you have to get the car to a dyno tuner to do it. A chip will probaby be your best bet. Again, I recommend Superchips Tuning, but there are other places that will burn a custom chip for your application like Diabalo, Autologic, and others.
Another thing I recommend is if you don't currently have one, I recommend getting a transmission cooler. Heat is the number one killer of automatic transmissions. A cooler will help to reduce the transmission temperature and provide longer transmission life. Once you get aftermarket gears, you will definately need one of these.
If you have any other questions, just let us know.
Anyone else know for sure if he can just do the speedo gear swap?
