I posted this in another place as well, but it seems pertinent to both.
I developed a rare shudder at 25,000 miles. With research I saw threads where the spark plugs had excessive gaps at 40 to 50,000 miles. So, being cheap enough and easy enough I decided to change my plugs. I did go with the standard heat range as I do not have a tune. This took less than one hour. Plugs looked a little black/rich but the electrode was gray. All gaps were between .030 and .031. A little residue on the threads, but all in all Probably a waste of time. The shudder was so rare that I won’t know for a while if it fixed it. Next change interval will be 50,000 miles. The plugs I pulled out were Ford CYFS12YPCT. The boots looked perfect, as expected at such low mileage.