Are you looking for that info for polishing or finding a repair or repaint ? There are many valuables in that question. For polishing you really want to know how thick the clearcoat is, because in reality that's what your removing and polishing to make it shine. In a repair or repaint there are huge differences in the thickness. You would need a thickness gauge to really see where the repair/repant was done.
These trucks are about 9mils thick, in that there is the clear coat and clear is about 1.5 to 2.5 mils.
There is some really crazy info on autopoia about the clearcoat and uv stuff, in removing to much clear. Because the uv inhibitors are in the very top part of the clear it will not block or disperse the uv and could start breaking down the paint. Crazy stuff.....