For my old Tacoma, a mr clean magic eraser always worked wonders on the black unpainted trim. Mines was almost a light gray, and no chemicals I tried ever lasted very long, but the magic eraser made it look brand new. You can tell it took layers of crap off the plastic and all that was left behind was clean and black.
Just an FYI for those that don't know. Magic erasers are a super fine grit sandpaper...