Just purchased a 2015 Ram 1500 Laredo 4 x 4 3.0 Diesel- after 17 yrs with a 2002 Ram 2500 4 x d 5.9 L Diesel. After reading the owners manual - discovered the truck will take 5W-30 Synthetic instead of the old 15W-40. I traded my gallons of 15W-40 back to Bi-Mart - and bought Mobil 1 . The question is what is the best synthetic oil for this vehicle ? All this is a new experience - my old truck went on and on for 17 years - but sounded like a log truck next to this 3.0 Diesel. It's like going from a Model T to a Ferrari !