Couple weeks ago changed the spark plugs in my 04 Escape 3.0 with 93k. I can't believe the difference in the way it runs. Shoot even the wife commented. The intake cleaning I gave it may of helped more than anything. Now on my F150 5.4L with 75k I changed the plugs and didn't notice a difference... guess that could be the difference in engines. What you all say would be the optimal interval for the changing the plugs? I was thinking 75k as a good number.