Don't waste your time or money. Flattening paint is pretty much just a matter of additives that disrupt the surface finish, essentially making the top layer slightly rough and porous. Once you go beyond the normal "flat" finish and begin getting into the velvet look, your paint will have no durability left and the slightest touch will create obvious "scuff" marks. Not to mention how easily it will capture dirt and simply cleaning it will mess up the consistency of the finish.
Trust me, if you go beyond flat or even beyond satin you'll regret it in the long run. And no level of blackness or flatness is going to make your truck disappear at night so don't bother trying. It will look cool for 1/2 a day then look terrible in a month, unless you store it indoors in a plastic bubble. ( and make sure you don't let the bubble touch the surface when you stick the truck in it! ) and you won't have any money left over to repaint it a month later.