Almost from the time I got this car, last November, I have had an intermittent vibration/roughness in the drivetrain, usually noticable after the car warms up. The engine fan cycles on excessively, although the temp gauge remains nominal. The car seems to lack torque when acting up, and does not readily downshift when throttled. Even fuel consumption seems to go up. Believe it or not, I have had 3 dealership service departments evaluate it, a Regional BMW Rep drove it as well, and no one can figure out what I'm complaining of. It seems like a tranny problem to me. Problem is, it is intermittent, and needs to be driven for a while to detect. Any thoughts, or recommendations for performance-oriented service outfits in the Washington DC area? It's getting to be a real drag to drive this car knowing something is amiss.