OK Here is My 2 cents worth. Cummins says 15K for this engine on service intervals, but they don't warranty it Dodge does. Dodge says in their manual 7,500mi even if using synthetic. So here is what I do. I run the Amsoil 15-40 synthetic in the summer and the series 3000 5-30 in the winter. I run an analisys @ 7,000mi (It always comes back fine) I change the Fleetguard Stratapore filter @ 7,500mi & add 1qt. I dump @ 15,000mi & run another analisys(always comes back perfectly good oil!) The results are the same with either weight oil, It is good @ 15,000 miles. My rational is that if I have an oil analisys and the oil is good, Dodge would be extreemly hard pressed to not honor warranty coverage based on failure to change when they reccomended. Especially when a complete change was done within the normal service interval of the engine manufacturer and supported by hard data!. (Who by the way would run that long with DINO! oil & not think anything about it. ) When I reach the 100K mark, I will then switch to the 7,500 mile filter change / add 1 qt, analize @15,000mi, 22,500mi filter + add 1 qt & Full change + filter @ 30,000 mi routine.