My Current '99 F150 with the 4.6 gets Citgo Synthetic 5w30 on a 6000 mile OCI. Currently at 131,000 miles on the odometer, no engine issues ever. Previous oils included Valvoline Durablend 5w30 up to 70,000 + miles on a 3000 mile OCI, Havoline 5w20 with increased OCI to 5000-6000 miles for a year, and Rotella T synthiec with a 6000 mile OCI for a year. The 5w40 seriously dinged fuel mileage, with little benefit according to UOA.
Previous truck was a '97 F150 with the 4.6. Sold at 163,000 miles on the odomoeter. Valvoline Durablend 5w30 from new to sale on a 3000 mile OCI. No issues...