Make sure that the new plugs are not overtightened. Ford made a mistake when they designed the heads, and did not allow enough turns in the aluminum for the spark plugs, so they only go in something like 3 turns, and many back yard mechanics overtighten them, and bottom out the plug, stripping away the tiny amount of aluminum that hols them in place.
Use a torque wrench, or the Ford dealership. They are well known for poping out of the heads a few hundred miles after being replaced.
I would stick with the Ford spark plugs, they seem well built. it is not like the 60's when oil fowling the plugs was a problem in engines. My 2007 Ford does not use 1/2 quart in 6,000 miles. Engines are a lot tighter than the 60's and 70's.
I was reading advertisements from the 1950's in Popular Mechanics. I guess that engine rebuilds happened every 75,000 miles back then! Now it is not un-common for a car to go well over 250,000 miles, even trucks are going 175,000+ miles between rebuilds!
Good luck,
Fred.
