I had my painter do it. He sanded the sh*t out of it and used self-etching primer. I have a thread chronicling my journey in the color-matched grill war.
http://www.tahoeyukonforum.com/threads/color-matched-denali-grill.79831/
http://www.tahoeyukonforum.com/threads/color-matched-denali-grill.79831/