Ford changed oil recommendation to 5/20 about 2003 - supposedly for better fuel mileage. I ran Amsoil, then Mobil 1 for 123,000 miles on my V10 in a class A. I'd an Amsoil bypass filter, plus regular filter. Changed regular filter and sent sample to Oil Analyzers every 7,500 miles. Would get a recommendation to change oil around 35,000-45,000 miles. Had engine top end tear down at 127,000 miles due to spit plug. No measurable wear on lifters.
Given that the cost of analysis has risen to about the price of 6 quarts of oil my experience would indicate oil changes at whatever point beyond 7,500 miles you are comfortable with.