Your brand or type of oil doesn't dictate your oil drain intervals, the level of crap getting into said oil does. Stick with the original oil drain interval set by Ford when your truck was built. The engine doesn't care how much you spent on the latest gold plated synthetic oil, the additives that deal with the acids, unburnt fuel and sludge generally are the same regardless of the base stock, as a result the drain interval remains the same. The engine won't run cleaner because you spent more money on oil. I had this conversation recently with one of Mobil's engineers, she was telling this is one of the most common misconceptions about synthetics oils, there are only two oils on the market designed with the sole purpose of extending oil drain intervals in mind.
