I think rear axle ratio has something to do with engine life.
My F550 with 4.88 is on it's second engine, replaced at 105,000 miles.
It didn't blow up, but developed a knock that was audible on deceloration.
I didn't want to be stranded somewhere out on vacation with the 5th wheel so I elected to replace it.
Bfife's F550 is on it's second engine too. He bought it that way from the government and it was replaced somewhere in the 30,000 mile range according to the report when he bought it.