To improve the shift quality by keeping up the line pressure between automatic shifts (and firmer shifting itself), it is recommended that all automatic cars get an ALC. It is easy to install, and takes no more than 30 minutes.
The hardest part is getting off the screws that connect the stock line controller. I heartily recommend you have a socket wrench. It is near impossible to get it off with a screwdriver.
Click Here for a great link for the procedure on installing.
Here is an overall shot of the ECU (upper left box), stock automatic box (right hand side), and the HKS ALC (lower left hand side). The multicolor wires are part of the ALC.
Closeup of ALC (the foam was added to protect the unit; it does not come equipped this way):
Closeup of stock automatic box: