2004 Chevy Impala Transmission service

I am a self maintainer of my auto's since I got my first car. I bought a haynes repair manual for my car. It shows that I have a transmission filter. I want to change the filter (and pan gasket) and the fluid. I asked a service professional at a commercial shop about using a machine to pump out all the tranny fluid. I asked him about the filter, and he said that I did not have a filter nor do I have a gasket, but instead I have a screen. My question is: Do I have a transmission fluid filter and pan gasket? How much fluid is drained by changing the fluid by removing the pan? Is it better to have all the fluid pumped out? 2004 Chevy Impala LS 3.8L

Thank You,
Dan