Kind of depends on what you're doing with your truck and what you're looking to gain from your potential upgrade. The rear brakes do a lot less of your truck's overall braking than the fronts, so the gains from either upgrade won't be as dramatic as the front. If your primary concern is stopping power, then pads would likely be enough, since the pads themselves are mostly responsible for the increased friction that brings the truck to the stop. If you're concerned about fade resistance when out doing truck stuff, then you'll want to grab rotors, since it's the drilled and vented rotor design that helps dissipate braking heat.