Here's what happened one day that I decided to get crazy and give my grill a face lift.
The old:
I needed to blast the bits of bugs out of the little crevices so a few quarters at the self serve car wash did pretty good. To remove the oil based road residue I spraying it with brake clean iirc, or something that didn't leave a residue then let it dry in the sun for a while. Next thing was find a comfy spot to spend several hours with masking tape and a razor blade to mask off all the little chrome strips and other trim.
I taped off everything and sprayed the flat black first. Some kind of Rustoleum product. I used no primer cause the old plastic seemed like it had some texture to it...prob from the sun. After the black dried I cut out the GMC letters and sprayed them with the same 1620 Duplicolor Orange I used on the new engine in my 77 K5. Here's what I ended up with.
It's been two summer road trip seasons and somewhere around 5000 miles and so far so good.