Up until about 90,000 miles I ran Ford Motorcraft Oil 10W40 in mine. When the price of gas jumped up I swapped over to Mobil 1 Full sythetic, that winter my 4.7 started to "tick" on cold starts. Once the oil pressure built up it went away. I went back to the Ford MotorCraft Synthetic Blend and have used it along with a WIX filter for a long time. Just recently I changed over to the new formula Rotella Oil.
I asked the same question when I switched to Mobil 1 Full synthetic, should I really have any problems? Other than a little bit of gas mileage increase I didn't really show much of an improvement. Although my WJ has a lot of miles (140,000) on it so take it for what its worth...
http://www.youtube.com/watch?v=P5UMT6Tob9Q