I don't think 3K is anything necessary. OTOH I don't think these 9 MPG beasts with fill capacity of 6 quarts are really suitable for very extended changes even on best oils. My thought shoot for about 5K miles with synthetic. Usually that is about a year interval. If you travel on long trip, going over that won't hurt occasionally..8000 miles etc. on synthetic. Be sure to check level though. Realistically I don't think the oil lubed moving engine parts will be the eventual failure mode of my RV.