Hi Eggy,
I've been a bodyman for 15 years and have seen this many times and from different things, such as fallout from foundaries or any type of manufacturing facility, even the metallic from your front brake pads can fly up on the sides of your truck. The best way to get rid of this is to buff it off with a machine buffer, with a somewhat aggressive compound.It usually is a 2 or 3 step process involving a couple types of compound so swirls get eliminated. The dealership you bought the truck from should be able to do it, the only problem with that is they will have the cleanup kid do it most likely, and they are usually, well, lets just say not as skilled. I'm sure you don't want your new truck full of buffing swirls, or have them burn through the edges of the paint, the factory doesn't put any more clearcoat on then they have to. So just be careful about who does it, preferably one of the guys in the body shop. Hope this helped you a little.
Randy Scott