James, I've found that none of my older Mopars (and that's 1993 and older) likes platinum plugs, even the Autolites. A rough idle was the most noticeable undesirable effect. And with standard Autolite plugs so cheap (and all but one so easy to replace), the result seems far more satisfactory overall with the non-platinum plugs, from my experience. Chris in LA 67 Crown 78 NYB