I am about to take a long trip from California to the mountains of Colorado. Heading through the hot deserts of Nevada and Utah. My 03 Ford E350 4x4 van has 7,500 miles on the 5.4 liter V-8 engine. I have been using Motorcraft 5w-20 oil. With the heat and mountain terrain, I would value opinions about switching to Mobil 1 5w-30 or 0w-20 oil. My previous 2 Ford vans both went 200K+ miles without engine problems, and I hope to get the same out of this new 5.4 liter engine. Thanks!