It seems you have maintained your Durango in good fashion. The plugs in use these days (iridium, platinum, etc) are pretty resilient. Unless your application includes gobs of idle hours, I wager you will be fine to the 125K mark. Others who have Gen 3 D's with the V6 will chime in with their experience. I ran the Champion Coppers in my 04 Hemi to 50K without issue. Since they are a whopping $2 each, I figured 20K over spec was a good time to swap them.