I have been on two different Jeep web pages to build your own. On one sight if you chose the auto you can choose a 3.21 or a 3.73 gears. The other web page if you choose the auto it removes the 3.21 and gives you the 3.73. I am looking to buy a JK and want the 3.73 gears and I cant find one on the lot with the 3.73 but if they come with the auto I wont have to order them. So what do you get with the auto 3.21 or 3.73? And is a good idea to get the Track Lock option?