Jimm 12/18/2012Better to change both the fluid and filter (if equipped). The 4T80E transmission has two filter screens that are serviceable - inside the oil pan. These are removed and cleaned during the trans service. No need to remove the entire transmission for the fluid service.
Just drain the transmission normally via the bottom pan, or by using a suction pump and hose length into the fill plug hole on the side of the transmission.