Alvin and the Chipmunks - Season 5 - Eps 3: Sincerely Theodore
Theodore goes on a diet so he could go on a date with a pen pal, who is also one of Alvin's biggest fans. Things go wrong when Alvin finds out that Theodore's date is actually the daughter of a famous film director. Alvin then takes her out instead, breaking Theodore's heart. In order for Alvin to make it to his play and the date, Alvin gets Theodore to switch back and forth to his play and on his date.
About Alvin and the Chipmunks

Title: Alvin and the Chipmunks
First Air Date: 1983-09-17
Last Air Date: 1990-12-01
Status: Ended
Rating: 6.8/10 (from 74 votes)
Language: EN
Seasons: 9
Total Episodes: 172
Network: NBC
Genres: Animation, Comedy, Family
Production Companies: DiC Entertainment, Bagdasarian Productions, Ruby-Spears Productions, Murakami Wolf Swenson, A-1 Productions
Synopsis
Three chipmunk brothers, Alvin, Simon, and Theodore are adopted by human, Dave.
Cast

Ross Bagdasarian, Jr.
Alvin / Simon / Dave Seville (voice)

Janice Karman
Theodore / Brittany / Jeanette / Eleanor (voice)

Dody Goodman

Nancy Cartwright

Frank Welker

Tress MacNeille

Ross Bagdasarian