TT stands for Thelma Todd.
CBS paired the series with rebroadcasts of Norman Lear's classic series All In The Family, which ranked higher in the ratings by a wide margin. After Sunday Dinner's cancellation, CBS continued to air All In The Family with moderate success.
The series was inspired by Norman Lear's marriage to his wife Lyn, who is much younger than him. Lyn actually served as the show's co-producer with Lear.