you forgot thermostats, water seperator, and fuel filters.... on the HPDIs there is a high pressure fuel filter that clogs up quite often. its around $100 if i recall correctly. also, if that inline high pressure filter clogs up, its a good bet you will have to drop the VST and change the filter that fits on the bottom of the electric pump. so yes, the HPDIs are more expensive to service if you change all 3 filters. and every couple hundred hours you can expect those high pressure filters to jam up with dirt, if you dont change them. not to mention hpdis have to been known to foul up spark plugs if you do a lot of idling, and the plugs for them are expensive!