I had the exact same problem, went to satan and got a passenger side motor mount (you might need more than one)for about 50 bucks and some change. It cleared up the problem. Good as new. The reason I believe it causes this vibrating is because the motor torques up when you accelerate and because the side of the engine is not mounted properly it lifts everything including the axle and throws off the balance of the the transmission... ie....one straight shaft(left axle) and one at a small, acute angle (passenger side) both spinning and kind of like a gyroscope it throws the whole thing out of balance. Sorry for my horrible ability to type what I mean, butt i hope this makes sense.