Ford has had pump issues with heavy oils in the modular engine family, especially with the 4.6 SOHC engine. They especially had those problems with the 3.0 in the 99 model year.
Back to what I said in the first place, the engine was designed from a clean sheet of paper with thin oil in mind. 5W30 works so well that there is no reason to use anything else. If I were to use something else, it would probably be 0W30.
A lot of people use HDOE (Heavy Duty Engine Oil, or diesel truck oil) (Rotella T is such an oil)in their gasoline engine with good results. It has a much more robust additive package and has been found to be compatable with gasoline engines, or better said, there is nothing about it that is incompatable with gasoline engines. It would not be my first choice, but I would not be afraid of it. There is a big group at bobistheoilguy that endorse it.
