I used Mobil 1 full synthetic high-mileage 5-30, the weight spec'd for my 04 4.4i. I've always used Mobil 1 and no problems after 21.5 years. I went to the high-mileage variant to protect the seals and gaskets... still only ~48k on the clock. I change the oil every year, even though annual mileage has been between 1k and 2k for 10+ years. Perhaps unsurprisingly, I've never had to add oil.