Aluminum parts won't make a bit of difference in speed. If anything they will make it slower because of the weight gain. The only thing that will make your truck go faster is the engine and drive train. A .21 might make it go 60, if you can get gears to gear it high enough. With the stock gearing a .21 won't make any difference in top speed, but it has a lot more power to allow you to gear it up.