A modder known as theNGClan from the GTAForums reportedly uncovered data that strongly suggests that a North Yankton DLC is being developed by Rockstar.
North Yankton is an area that is generally inaccessible by players throughout the majority of the game. However, it is available during the beginning mission in addition to one segment near the end of the story.
Through digging the lines of code, a list of radio stations and weapons for this DLC were revealed. Michael and Jimmy is also noted to have dialogue and interaction in this DLC. No word on the other characters from the game.
The most exciting tidbit players are most excited about though is the possibility of running into Niko Bellic, Roman and other characters from GTA IV.
Rockstar still hasn't confirmed the existence of the DLC, but we will definitely report any new information that comes up.
Grand Theft Auto V was released for the PlayStation 3 and the Xbox 360. The next-generation and PC versions remain unannounced.