I was coming home from work and i saw another gmc dually driving the other way and his rear bumper along the side and ended when the hump flattens out. Does anyone have any idea what im talking about and if so who makes that rear bumper?

I know exactly what you are talking about, but google is not my friend right now- couldn't find anything.

http://www.ranchhand.com/products.aspx?year=2007&make=Chevy&model=3500%20Dually&description=Dually%20Back%20Bumper

http://www.ranchhand.com/prodpix/BumperDuallyMounted.gif

This is just one of them.