I'm working on my fiance's daily driver 2003 sunfire with the automatic trans.

The car has about 90k highway miles on it, and I'm looking to change the fluid in the transmission.

How many quarts of fluid should I buy if I am just doing a pan drop, clean everything up, and replace the filter?

I'm looking at using the Maxlife fluid that meets the GM spec Dex III.

Is it usual to drain and refill these transmissions or should I have it flushed at a shop?

The trans shifts fine no problems right now. I need the car to last her another year then she wants something new.