I have Motorcraft 5w30 syn blend in my 06 Ford Ranger 4.0. The oil has only about 2k miles on it, but it's been in there for 6 months. The truck has NOT been used for short trips. Whenever I used it, it was ran on the highway for a good 20-30 min. The rest of the time it sat in the driveway, which needless to say, was most of the time. I have a 5 qt jug of M1 0w-30 ready to go in, but I don't know if I should keep the Motorcraft in for a while longer.