I'm currently nearing the end of a second Auto-Rx application on my truck. Current odometer reading is ~99,500 miles. Previous oil used has been Mobil Drive Clean 10W-30 and that's what's in the truck right now. I've never done a used oil analysis on this truck and it's currently seeing 450 miles of commuting per week all on rural two-lane highways (with a few small towns thrown into the mix). Questions. 1. I'd like to stretch my oil change interval. Previously the truck only saw 5,000 miles per year total and I changed the oil every three months (lots of short trips). I have a lot of Mobil 1 10W-30 in stock ($3.39 per quart at Target) that I use for my supercharged Camry. Does a quality dino oil changed every 5,000 miles make sense or would the synthetic make better sense? It does get down WELL below zero in my part of the country. 2. How far should I go before doing an analysis for both scenarios (dino versus synthetic)? Thank you for your help!