Took mine down to a monument company where they make headstones. Sandblasted the whole thing, top, bottom and all sides. It sure took off the crud too. It is thick enough to tollerate it without any ill effects except it's a very convoluted and angular surface to re-shoot during painting. I'm still finding places the painter missed, like the pockets and under the rails.
The rest of the truck was also blasted, all except for the hood and inner door panels. We both thought they were too thin to try it on.