Go to www.tccoa.com and read up on their transmission articles for the 4r70w automatic transmission. I know its a Thunderbird and Cougar online club but the 4r70w is whats in our cars just like the T-birds.
I recommend the following for a serious automatic:
Torque converter - Go no less than 3000 stall or you will be disappointed
Transmission cooler - The bigger the better. Be sure to get a fin design to as it cools better.
Shift kit - I recommend the Jerry mod shift kit as it is designed specifically for this transmission but a good aftermarket valve body will work as well.
Gears - No less than 4.10's for a n/a automatic. I have 4.30's in mine and love them.
EEC Flash or tune - I recommend this as it will help to correct line pressure, torque converter clutch locking sequences, and shift points, but you will need one or the other when switching to different gears to correct the speedometer and to get the shift points correct. I recommend SCT tuning.