Originally posted by Troy Destroy:
the PO painted it a very nice dark grey metallic
If it were me, and I liked the color, and had half a gallon of paint, I'd give it one more shot and see how it turns out. It won't cost you anything but time. I'm assuming if you have two quarts of paint that it's acrylic enamel. Wet sand the entire truck with 400 grit paper, and clean it really well with soap and water, then wipe it down with wax and grease remover and give it one nice even coat. Then if you don't like it go with the black primer.
In the end it's your baby, do what you want, that's just what I would do.