I have a 2004 Pathfinder 3.5L that sputters when I give it more than about half throttle, it runs smooth if I accelerate slowly. It's been doing this for at least 3 months now and I still haven't found the problem, I've checked the front cats and changed the fuel filter so far and it hasn't solved anything. Its about to hit 156,000 miles. Any help or advice would be appreciated