My 99 JGC hit 100K miles so decided to change spark plugs, thinking they were platinum. Was amazed that they were copper core and lasted that long. Two dealers said to go with platinum, my dealer said Jeep does not recommend them. Found an article that said the platinums are incompatible with the setup with a coil per plug and can confuse the computer due to potential reverse polarity. I want long life but don't want to screw up the vehicle! What's the real skinny?