We had our 2006 Stag with VQ25DD decarbed at 120K by our local Nissan dealer just over a year ago and it came back with an intermittent miss at idle progressing to a nasty stagger on acceleration a month or so later. It was far worse than before we took it in. It went back to them 3x times and nothing they did fixed those problems and they investigated all sorts of stuff including coil packs etc, but they were sure it was nothing they'd done. Eventually, several months later, after losing all faith in them, we took it to a specialist in modern engine problems. It didn't take long for him to find that one of the new spark plugs Nissan had fitted had a cracked insulator, and was tracking, and was obviously caused when installed. By that time, I'd had enough of the petrol bills, and the lack of expertise by the local agents, so it was sold. I'd recommend staying well clear of the 250DD and 300DD if you can. Apparently injector failures in these motors are common and expensive too - around $3K upwards.