Good morning BITOG! Long time member here but haven't posted in awhile. Looking for some input on oil for a new 6.7 F350 dually. I tow a 42ft 16500 pound fifth wheel with it. Mostly tow around Texas so no big hills. The truck is a tow vehicle only so no daily stop n go driving. It's a year old with 4500 miles. I want to stick with Motorcraft oil for personal reasons. I have used the MC 5W40 synthetic for the last year but switched to the MC 15W40 on the last change. The OLM drops like a rock with all the sitting that the truck does so I hated the $ 200 synthetic changes with minimal mileage on the oil. Will I be ok with the 15W40 dino oil? I'm sure I will but just looking for others experience with 15W40 and heavy towing in the heat. Thank you.