I have a 2009 G37X coupe with 74K miles. While driving it the car will not let me go past 3000rpm. When I get to 3000rpm the engine and transmission seems to hit hard and jerk around. Thats the best way I can describe it. Otherwise, the car runs and drives fine at a low rpm. I have taken it to a dealership and had all the sensors replaced. That did not fix the problem. They say it could be the timing chain guides. They want 4700$ to change the guides. They cant guarantee that is the problem. Has anyone else experienced this problem? I would like to hear any feedback before I invest that much money into the car.