The vinyl decals came off my black truck in 15 minutes just from teh heat of having it sitting in the direct sun. A bit of goo-gone to take up the little bit of adhesive left behind, and you can't tell they were ever there.
The plastic molded ones should come off the same way. A heat-gun, or hot hair-drier, something plastic to pry under them with (the vinyl decals come off with a finger-nail, but you need a bit more grip with the plastic ones). But jost go slow, and be patient.
And use the goo-gone to remove any leftover adhesive.
Once removed, you should wash the truck immediately, and wax it well (hand/orbital with carnuba), because there is NO protective wax between those decals and the clear-coat on the paint.