Any suggestions on when and what fluid & filter to use to best protect my transmission? I have been told MOBIL 1 is good. I have 46k on my TB. Current fluid looks and smells good, but 50k change maybe a good idea? I drive in Houston traffic daily.
Any comments?

Check your owner's manual see if Dex 4 is recommended, if so Valvoline Max life Dexron is a substitute, if not any good brand Dex 111, use an oem filter, gasket should be the reusable type. Full syn is not required or GM recommended.

Like my 2005, your '04 probably specs Dexron III (H). I think you'd be hard pressed to find a dexIII not be 'H" certified these days. FWIW, I did a pumpout and refill with a case of Napa 'premium merc/dexIII' a few thousand miles ago on mine. She shifts like new.

Joel