Along with Ford, the new 6. 7L uses urea also. We ran our new Ford F550s 3K miles on the first oil change, we reset the oil life monitor, and are going to run 5K this time. If everything goes ok, will probably got 7. 5K on the next oil change. Ford reps. have indicated to us that there is no mileage recomendation on oil change interval other than to do it when the monitor says to.
Most likely, we wont go past 7. 5K due to the urea tank being low by then. Don't want to have to haul a jug of that around, have enough crap on my truck already.