Using the royal purple is not what will or may void the warranty. Its going 12 to 14k between changes that can get you in trouble. If the truck has an issue that is oil related as in wear on the engine or build up that can be possibly linked to the oil change routine then they can decide not to cover the repair. They cant void the entire warranty, just decide not to pay for a certain item they deam is related to the oil change proceedure. In other words they cant decide to not fix your broken axle because you used royal purple and went 12k between changes. That is why the oil manufactures tell you to use the recommended mileage on changes. I use the Royal purple and am happy with it. I let it go 12k but change the oil filter every 6k
).