My 2000 Tundra v6 3.4 had some hesitation when accelerating which got worse over a 30 day period. My check engine light came on which turned out to be a misfire on cylinder 1. Can't remember the last time I changed the spark plugs, but at 257,000 miles it won't hurt. I now have a smoother ride and of course better gas mileage (18.9mpg average). Will buy them for my wife 97 4runner with the same motor size.