That's interesting! In Australia, the Navara that the Titan was borne from was always a 4 cylinder turbo diesel. Other markets using the smaller turbo diesels is what inspired Cummins to bring out their 4 cylinder crate motor in the US for project 4x4 swaps. The idea is they're a great alternative to petrol V8s and a much more efficient and lightweight package than a Cummins 6 or 8. You can get all the torque you could ever want for 4x4 out of a 2.5 litre turbo diesel, and they'll fit in anything. I suspect the Titan is more aimed at towing though, so no surprise they've got the bigger Cummins.