On the oil issue"The potential for further savings through extended engine oil change intervals surfaced following laboratory tests that showed dramatic reductions in lubrication oil contamination in the ISX-G. Beginning in December, Cummins Westport engineers will institute periodic sampling of oil quality in the new natural gas Norcal trucks to further define oil life during on-highway operations. A typical Cummins diesel fuel ISX engine requires a $320 (US$200) oil change approximately four times a year."
$200 sounds low from what I have been hearing. From what I understand, with natural-gas there are potential savings of thousands of dollars per year on oil changes .