You may be able to get high miles from a properly maintained Ford V10 ... but the 5R110 5-speed (6 speeds internal) computer controlled transmission linked to it may be another story.
Last summer when going out our driveway beginning a 10,000 mile trip across the U.S. in our 2005 E450 small (24 foot) Class C, the transmission started to fail. Temporarily postponing our trip, we limped into town directly to a transmission shop. The transmission fluild level and color was fine. I even had the fluid changed at around 25,000 miles. A couple of clutches in the tranny had failed for some strange reason with onlly about 51,000 miles on the vehicle. Instead of waiting the several days for them to rebuild it, in a couple of days they had installed a heavy duty option remanufactured 5R110 transmission and we were on our way. The remanufactured transmission seems to shift smoother and is in general more well-behaved than the original one ever was. Maybe whatever is different in a heavy duty build is the reason for the improved performance.
A blown transmission in our 2005 E450 after only 51,000 miles was a real surprise to both ourselves and the transmission shop. We have no idea what we could have done or not done to make it fail. The remanufactured transmission has a 3-year unlimited mileage warranty.
