I discovered a strange jerking when the vehicle is agressively accelerated from a stop. It is like the engine is missing but it is not. It only showed up when my wife wanted to see if it would sqeal the tires from a stop sign. It showed up again while going up a steep incline where it shifted into low gear. It only occurs under hard acceleration and steep inclines when the engine accelerates to about 3 grand. It doesn't happen under most driving conditions. Any ideas?