I have a 2010 Murano SL with just over 148,000 miles on her. I replaced the tranny about a year and a half ago (maybe 15-20,000 miles ago) and now I'm having issues again. Car idles rough, like a motorcycle, and when I accelerate the car starts to knock/thump. I thought maybe cylinder misfire but mechanic said the catalytic converter needs to be replaced, which isn't exactly cheap. You guys think its worth it to go ahead and do it ($1200-$1500) or is it time to say good bye and move on to a new car? What would you guys do?