I have a 2015 F150 4x2 and when I have the tires rotated every tire dealer including the Ford dealer, rotates front to back with no crossover. I have the tires rotated every 8000-10,000 miles.
My 2015 F150 manual specifies 75w-90 so I put in Mobil 1 75w-90 full synthetic. Now Ford is back specifying 75w-140 for all the axles, but I am not going to go through the trouble. 80w-90 is just fine too.