Bought a 2000 F350 with 112k miles, done a few oil changes and currently at 120k. Considering changing to a synthetic for the long term, like to keep the truck going for a couple 100k more. What are you using and what change intervals? I use my truck as a daily driver and occasionally tow a 10k 5th wheel. Been using Dello 15w 40 at 3k+ oil changes. Thanks.