Manifold/header/muffler/tail Pipe problems of the 2010 Jeep Commander

The car drove fine pulled it in the garage. Got up Thursday morning to go to work the car turned on and started shaking and I turned it of tried once more it would not turn on at all. So then I changed the crank sensor the cam sensor got a new battery put new spark plugs the truck still would not start. Had a garage look at it they said it was the intake manifold so they therefore told me to take it to Jeep because it was covered under warranty. I took it to Jeep and the told me this would not stop my car from running, they have had my car for a week and no diagnosis. This car is only three years old but Jeep customer service says to me you bought it used so you dont know what was done to the car. So I say to her your qualified mechanics you have working at the dealers cant do the job. What great customer service Jeep has. And the dealer is suppose to be getting in contact with Jeep techs in corporate to try and figure out what the problem is. Still no car 6/01/15.