I just replaced plugs in a 2014 Ford Expedition at 70,000 miles. Owner was complaining of a stumble at speed when he would give it a touch of gas and worse when A/C was on. He bought an inline fuel filter, which NAPA sold him (It has a non serviceable filter in the tank). After changing the plugs, he said it felt like it had more power, but thought it was in his head. Let his wife drive it and she asked what he did because it felt like it had more power. Just because the owners manual may say 100,000 miles before they need changed, it's not always the case.