There is probably something wrong with your car. mine is plenty fast, and runs 14.8 1/4 miles all day. The 2.82 diff will totally transform the car. I went back to stock on mine and its still plenty fast. The transmissions eagerness to upshift is probably what gives the impression of being slow. When you floor it, hit the kickdown switch below the accelerator pedal and it should scream.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K