Would the dealer legally have to replace the vehicle if im not happy?

I bought a brand new vehicle from a ford dealership. It didn't even make it half way to the first oil change and it broke down. It only has 1301 miles on the truck. The Smart Junction Box went out and the rear end had started leaking. The truck is completely out of service because of the smart junction box. Im having issues with the dealer getting the vehicle fixed. They keep telling me that the parts hasnt showed up yet. They say they dont know why my part keeps getting delayed. They have had the truck over 2 1/2 weeks now and im very frustrated with the service. I feel like that they sold me a lemon. Its a 2010 Ford F-150 SuperCrew. What classifies a vehicle as a lemon? How long are they allowed to mess me around before i can do something? And what can i do?