My SO is a paramedic and a few years back, I don't remember the model year, the ambulance company she worked for replaced all of their Ford chassis 7.3's with the MB Sprinter. 8 units total. The paramedics loved the room in the back and the company loved the better fuel economy, but....
These ambulances are used mainly from rural areas to the nearest trauma center 65-70 miles away via interstate highway. This means these unit are either running at idle, very little on city streets, and then full throttle all the way to the hospital up the interstate.
A few months later and with none of the 8 units reaching 100,000 miles, all 8 engines failed. They just wouldn't hold up to this type of usage. How long will they last in RV service? No idea, but at full throttle for miles and miles, they weren't up to the task. And yes, they were maintained properly.