I agree that the step rails are aluminum. I beleive they are powdercoated, but could be wrong.
As for cleaning your wheels, make sure they are cool to the touch and just use soap and water and a sponge. Most of the "Quicksilver" type cleaners will be too harsh on the finish in the long run. Since the wheels are essentially painted, you might want to wax them when you wax your truck too. It will help repel the brake dust and make cleaning a little easier.
As for tire shine, I use the Black Magic Tire Gel. It tends not to kick off a whole lot and if you rub the excess, off the tires just look clean with a slight shine, not wet like some products. Hope that helps.
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Jeb aka Ag Bullet
2001 Frontier S/C CC
www.nissanfrontier.net My Ride Most of the world's problems can be solved with blunt head traumas.