As Gromit added, the Fords are much cheaper usually in fleet situations, that's the main reason they have the market share.  And I do own an '01 SD with the 7.3 and like it.

As far as the Freightliner or International ambulances, we had 2 neighboring departments that went that route 3-4 years ago.  We talked with both before purchasing our last one and both departments were going back to Ford chassis.  Even with the air ride, the truck chassis' ride too rough, was the claim.  They are also harder to get in and out of, even though they 'kneel' when you open the rear doors.  I wouldn't have believed it if I hadn't heard it from several guys I trust.  I also thought the truck was the way to go.

Worth what you paid for it...

Mike