EBP (exhaust back pressure sensor) and/or EGR (exhaust gas recycle valve). Both are covered by the warranty however you need to get it to the dealer before you hit 36,000 miles otherwise you will have to pay the $100 dollar deductible which Ford charges on all engine related repairs from 36,000 miles until the end of the engine warranty at 100,000 miles.
To test the EGR you can unplug it. The worst that will happen is that the "Check engine" light will come on. It is located 2 inches to the passenger side and 2 inches in front of the oil filter. It looks like the cap of a can of right guard with a plug in the top. Just unplug it and see if it runs better. If so, you probably have a carboned up EGR valve. You are at about the right mileage for this to happen.