C-10 Stock Chrome Rear Bumper

[My70C10]

I'm trying to figure out if the my rear bumper is bent. When looking at it from the side the license plate holder is tilted so that the bottom edge is further from the end of the truck than the top. I also noticed that the top edge of the bumper is curved...like a slight frown. When viewing from the rear, the ends of the bumper appear to turn down slightly. I have tried correct this by loosening the bracket bolts and pulling down on the bumper but no joy. Does anyone know what the stock appearance should be or can point me to some pics of one done right.

Thanks.