My 321T upgrade experience (both standard Exec Plat and as the transcon leg of a long-haul international itinerary) has been pretty good. Have never missed Y--J and get complimentary gate upgrades from (paid) J to F at least 50% of the time I buy a J class seat. Just recently upgraded around T+48 on an early evening post-Christmas JFK --> LAX. Exec Plat with <$15k in rolling 12mo EQD. AA.com seatmap had been showing 3 first class and 5 business class seats open a few hours before.