I have the 2:73's in my 02, so I assume I have the steel driveshaft Would aluminum or carbon fiber reduce the weight enough to give a noticable improvement in horsepower? I know with less weight on the driveshaft it reduces some loss to the rear wheels, but approx. how much?

 

Changing a driveshaft will not give you more horsepower. There is an extremely small chance that you might be a touch quicker due to the smaller rotional mass. But changing a driveshaft does not equate to more hp. You havent done anything to the engine, and the engine is what makes the power.