You need to educate yourself regarding the Lemon Law in your state. There is supposed to be a copy of the statutes for all 50 states in your glove compartment, but even if it is not there, you can certainly find the details after about 30 seconds of "Googling". The reason why I suggest educating yourself regarding the Lemon Law is because, in most states, after the specified number of unsuccessful attempts to resolve a mechanical problem (3 attempts is typical, but this varies from state to state), you qualify for a settlement, which could include a comparable replacement vehicle or a buy-back of the present vehicle (again, this varies).
So, keep taking it back to the dealership, keep all documentation of your complaint, and, if necessary, file for settlement under the Lemon Law. Also, since a stalling vehicle is inherently dangerous, I strongly suggest that you also notify The National Highway Traffic Administration (NHTSA), via their website. Once a particular defect is statistically significant, they can mandate a recall of the vehicles in question in order to provide a free repair to owners--even after warranty expiration.