Rumors and Leaks
Rumors and leaks of Grand Theft Auto 5 details have slowly began to fill the vacuum of information surrounding GTA5. This page collects unconfirmed -- but plausible -- Grand Theft Auto 5 rumors, along with appropriate sources for each.
Vehicle List Leak
On May 15, 2012, it was discovered that the Max Payne 3 disc may have information on Grand Theft Auto V's vehicles buried in its source code. This has happened before with Bully and Red Dead having source code that contained Grand Theft Auto information.
A full list of vehicle names has been extracted from the code and posted below.
Release Date Rumors
A release calendar leaked by "a major UK High Street retailer" suggests an Autumn 2012 release window. 
Sterne Agee financial analyst group predicts that GTA V will arrive in early 2013 to allow Rockstar extra time to polish the game. 
A picture of a flyer from Canadian retailer Future Shop (taken by IGN reader Antonio LaRosa ) displays a release window of Winter 2012.
A listing on GameStop's UK site shows a 01/03/2013 release date .
Ex-Rockstar Information Leak
An Examiner article publicized a large chunk of GTA5-related rumors, stating the following:
"It has recently been brought to our attention that a poster over on the official GameSpot forums have posted a massive list of unreleased information about the future title, Grand Theft Auto V. Through a post, that has since been deleted by the forum moderators over on the GameSpot forum, along with the poster, a user by the name of Gloggle has revealed that he is a friend of an ex-RockStar employee that was fired for misconduct. Now, it seems that the ex-RockStar employee now has the intentions of leaking information on GTA V."
As for the information that was listed, you can find the post as a whole below or you can view a Google cache version here.
Warning: Number 8 on the list contains spoilers of past Rockstar titles (RDR and L.A Noire).
1. The protagonist will be one character, and one character alone. His name is (as some rumours said) Albert De Silva. He's a half hispanic man who was once part of a crime family in Vice City. He decided to settle down and have kids in Los Santos. He has one son called Kevin De Silva who is your stereotypical CoD player. He's lazy, useless and shouts racial abuse online and is really into FPS games. Kevin does admire his Dad though.
2. Multiplayer will hold 32 people on the Xbox and PS3. I wasn't told how many were able to be on the PC. Just like in RDR, players will be able to form Gangs. These gangs are not ranked through XP anymore, but via Reputation. Instead of gang hideouts, you can do jobs that range from robbing a launderette to breaking into a military base and stealing state-of-the-art weaponary. The Gang leader has much more control over his or her gang by being able to rank members of their gang and setting more specific objectives to specific members of their gang. Gangs can have their own terratory but this only applies to areas inside the city of Los Santos.
3. The map is about 5x as large as the GTA IV map and the City of Los Santos takes up just under half of this area (so it's a bit bigger than 2 GTA IV Liberty Cities). The map is (like most GTAs) seperated into three different sections.
4. Planes are flyable, they range from World War 2 fighter planes to Private Jets.
5. Cars and guns are customisable to an extent, for example, you can customise a gun to have a supressor on it and you can install nitrous into cars.
for someone matching your description. Some missions become unavailable if you are wanted.