What makes it rare, as the vin decoder showed, is the combination of all the options your truck has. Color, assembly plant, combination of options, etc.. It's not that it's a rare truck so to speak, it's just that there are only 3 with all of the exact same setup as yours has.
When I ran my 03 1500HD on there it said there were 2 like mine. I have seen others almost identical, but they will have a console where mine doesn't, or different radio configuration, or something small like that.
Hope that clears it up some for you. In all honesty though it is different from all the other trucks though because it has your name on the title.
