I just changed my stock spark plugs in my mustang to NGK Iridium TR55IX (i think). Took me a little over an hour to change them. There was coolant and whatnot all over the spark plugs in the recess. So drying that took a while. Finally got them changed and fired up. Ran much better. Much faster throttle response and felt like more power. Haven't really been able to get on it too hard. Its kinda snowy out =D Pretty expensive for the plugs @ 6 bucks each. But seems to work good. I put antiseize on them, and dielectric grease on them as well. Today i'm going to change my oil and filter. One thing is for sure, the Probe was a hell of alot easier to work on.