My son just had spark plugs changed on his '09 Tacoma that he bought new...after 182,000 miles, believe it or not. There was never any indication of any problem yet when the old plugs were pulled the electrodes were virtually gone, yet it ran fine. The kicker is that it doesn't run any differently with the new plugs, but he has noticed a drop in mileage. How is that possible? Did the trucks computer make adjustments for the plugs as they wore out over time, an adjustment that is not paired with the new plugs? I'm just grabbing into thin air here...any ideas? I watched a couple videos and at least two people changing their plugs mention that the passenger side and driver's side had two different types of plugs in their trucks. What's with that? Not just different types but different manufacturers also.