Part of the problem IS reliability problems with the the new emissions and how complex they are. They are not getting the mpg's they used too and the upfront cost AND maintenance is more.I've been known to work part time for the largest private ambulance service in America and we have just lately received 2 brand spanking new Ford PSD ambulances.
Gas motors will not provide the same dependability and level of care a diesel powered ambulance will & yes the gasser will be cheaper.
What's more important saving a few bucks or making sure that ambulance gets to where it needs to go???
I am a diesel guy too.