04 GT trany prob
 

I have a 04 GT with a 4R70W. the car has 48K on it and i have only put about 6K since i bought it. the tranny is really starting to slip when shifting from 2 - 3. I know i need to get it rebuilt. my question is this. if i need to go through it what upgrades should i have done to get a quicked shift and a longer life. it is my daily driver.
Thanks!