In all fairness, bio can cause issues in the right situation. It has a higher flash and vaporization point than regular diesel. We all know that there is always a little fuel that gets by the rings and into the crankcase. Most of it vaporizes in the heat and exits via the crankcase ventilation. Now, if an engine is not run regularly at full operating temps, like a lot of short tripping, bio with it's higher vaporization point can accumulate in the oil and lead to some fuel dilution. That is the primary reason some OEM's will spec a shorter OCI. Cummins doesn't state this on their heavier truck diesels, primarily because they know that they are normally not short trip operations. Those engines run for hours on end at normal operating temps. So there is no real reason for major concerns. The pickup diesels... different can of worms. If it is only being run highway miles and getting a lot of time at full operating temps, I wouldn't worry a bit. But if it is getting a fair amount of short trip stuff going on, then follow the OEM lead to be on the safe side.