I'm going to resurrect this thread because it's Easter season.
I have a 2011 GEN1 6.2L and changed the spark plugs in March of 2022. I bought them at a Ford dealership parts counter - their current recommended spec plugs: Motorcraft SP-526 also known as CYFS-12-FP. Since then I have noted measurable reduction in MPG - down 0.7 MPG. From March 2021 to March 2022 the calculated (not off the dash, but by manually dividing miles by gallons burned) was 15.5. After the spark plug change from May 2022 to March 2023 the calculated MPG was 14.8. 10 to 12 months of regular driving in both cases.
I did not write down the alpha-numerics of the factory plugs I removed, so I am wondering whether they were different from the new plugs that I installed. BTW, I meticulously gapped the new plugs to the recommended spec (0.044"), torqued them to the recommended spec (159 in-lb), and replaced the spark plug wires with new MDS wires. (I have also tested the new wires, and they're fine.) Unless there is a difference between the factory plugs and the new spec plugs, I am at a loss to understand the reduction in fuel economy.
Does anyone know what the original plugs for the 2011 6.2L Raptor were? Neither the 2011 F0150 Owner's Guide nor the F-150 Raptor Supplement include the plug spec. They both say to "see your authorized dealer" - which is what I did!