I painted mine (and yes, it used to be chrome)...
All i did was scuff it with some green 3m scuff pad..
Then cleaned it with wax and grease remover...
Sprayed a little bit of adhesion promoter on it just to be safe... (this stuff works waaaay bettter when its warm/hot)
After that, i used my airbrush and some black paint that i made and sprayed it on.
After letting it dry (the stuff we use for work is fast drying), i wiped off the overspray with a tack cloth..
then clear coated it..!!
It turned out great but if your truck is stock height like mine, it'll get chips in it and look funny after awhile..
Now i repainted it with bedliner spray from rustoleum ( cuz the bedliner spray matches the flat black factory plastic color) and it has yet to chip..
I would post pics, but i have none from when i did it..