I also have always used Platinum plugs, and I also have +2 Bosch in my jeep now, and it actually idles smoother, not rougher. Also, a lot of DODGE/Cyrlser motors have Mitsubishi motors (since 1984 that I have seen), and ALREADY HAVE platinum plugs, so you must be speaking ONLY Dodge/Chrysler with Chrysler motors, right? You did not get a Dodge Charger or Avenger in there with Platinums, then replace with Copper and the problem went away, because they COME with Platinum plugs. So, you would be saying, as we all know anyway, Chryler motors suck... Yep, Any 2.7, and just about any Chrysler motor that was not a 3.3 or better, or Straight or Slant 6... All their small <= 3.0 V6 motors BLOW... Every Chrysler product that has a Mitsubishi motor has run circles around the Chyrsler engined counter-part.
I know, I have seen it first hand with Family, we are all Mopar Men...