I owned a fleet of Kenworth trucks with aluminum dump bodies, wheels, fuel tanks, etc. I used a product from Valco which did a fantastic job. As Boot says in his post, you should have it acid washed first. Valco makes Aluminum Brightener which is their brand of acid. You can spray this on with a garden type pump sprayer (2-3 gallon size) then pressure wash it off. Then apply their Metal Polish. The acid wash is easy. The polishing takes a lot of work.