If you want to make the switch, do a synthetic blend oil change first, this will help condition the seals for a full synthetic. Older engines tend to leak if you just dump Synthetic oil in them. Some of the Fords call for 5w-20, but the early 4.6 and late 5.0's call for 5w-30. Lighter weight oil reduces drag on the engine resulting in increased fuel efficiency and performance. Just a thought. I run Pennzoil Platinum 5w-20 in my 1995 5.0 GT and it works great. No leaks, no decrease in fuel efficiency, no excess heat.