Greetings, Just bought a 1999 26' RV w/ Ford 6.8L V10 Triton w/ 89K miles. The owner of the last 3 years has used Valvoline Dino 10w40 but manual says 5W30. It has 1000 miles since last change. I'm going to be taking it this summer on 5K Road trip and thinking about going to full synth and just not sure. I use Mobil One 0w20'in my 2013 Prius V and Castrol Edge 0w40 in my 2007 BMW X5 so am a fan of synthetics. I at least want to use the Motorcraft 5w30 part synth that Ford suggests rather than the Valvoline 10w40 and a quality filter w/ silicone anti-drain back valve. Also should I consider high mileage oils? There are no leaks now. Was hoping some of you smart Folks may have some advice? Thanks in advance!