Castrol GTX Synthetic blend does meet the ford specs and have heard nothing wrong with it. You will be fine anything that meets the spec. Why do the your dealership highly recommend synthetic blend? It's just an easy across the board scribed recommendation. Consider the fact also that there is no Motorcraft 5w20 conventional oil. So that maybe a reason that they would make such recommendation. So if a conventional oil that meets the Ford specs, is it just as good as there synthetic blend? If you do not feel comfortable with going with a conventional, I recommend to go to Wal-mart and buy Pennzoil Platinum 5 qt. bottle. You will get a full synthetic at a good price. However, since your engine doesn't have a turbo or direct injection, you will be fine using the Pennzoil Conventional. They cannot void your warrenty for using it.