I have owned ford's for 65 years. I have always read the manual that comes with the car. The manual with my e-450 says 5000 miles between oil changes unless in very dirty conditions. To me driving on interstate and paved roads is very clean conditions. and as rv folks I think most of us are in clean conditions.
So i vote for 5K every time even though the guy that changes my oil puts a sticker in my window to change it in 3000 miles I still wait for 5000 miles and my vehicles never use oil. My 2002 explore with 140,000 miles does not require even a half of a quart to top it off between oil changes.