If it's a real chrome grille, you can't paint it. You can't paint chrome and have it last; especially with it being on the front of truck.
If it's the chrome look, that plastic surfaced chrome, strip it first. Use sand paper or when I was at the dealership, (I asked the same question because I can't stand chrome anything), he said they've had people use a power washer to strip the chrome coating (no idea if that is right). That pastidip is only going to give you an idea but it will hold up if you strip the chrome plastic coating first. My old pick up had a fake chrome grille and I sanded the hell out of it and plastidipped it and it worked great. I just don't care for the pastidip look as it looks sort of cheesy.