engine has a miss

Your car probably has the 4.6 Liter V-8 engine. This engine has a separate coil for each cylinder. It sounds to me like one of the coils is going bad. I had this happen to me, but it was most noticeable under certain conditions, such as climbing hills. Since the problem was intermittent, and only occurred under load, my mechanic hooked up his laptop computer, let the car idle, and it quickly determined which coil was bad. If you have extra coils (like from a "parts car") you can replace them all, or one at a time, to see which one is bad. New coils are expensive, so if you know somebody with a junkyard, you might try that option first.