First, I would question the premium costs for diesel that you mentioned since that will vary widely depending on where you are traveling. Right now here in OR, diesel is actually less than gas and I can use truck lanes thereby avoiding the otherwise mandatory full service attendant.
Other places we'll been in the West (excluding CA witch I avoid) the premium, if any has been minimal and is more than made up by better fuel economy.
Although I suspect you need to compare the benefits in coaches of the same size. If you want a 38' coach compare a 38' gasser to a 38' DP otherwise you data is skewed. Anything larger may preclude a gasser altogether.
