Check if LATAM (the new airline name) has an agreement with Alaska Airlines that allows you to check your bags all the way to your final destination. If not, all your planning goes out the window - you will have to leave the secured area and claim your luggage at Terminal 6 baggage claim, then proceed to TBIT to check your bags in at LATAM (Level 3). Further, LATAM may not take your bags until 4 hours before your flight.