The aluminum and the factory finish depends on the model year.
That being said, clear coat can be "buffed" with varying degrees of success, I am told. I have never tried it.
In my experience, clear coat cannot be "polished."
2007 Classic Limited 30 (Sold)
2007Chevy Silverado 2500 HD Duramax/Allison
Four Corners Unit WBCCI #8654, Affiliate NM Unit