The OEM height is typically higher in the rear to accommodate loads so that when you haul rather than squatting or "bulldogging" the truck levels out instead. The idea behind a levelling kit is to raise the nose a bit to level the rig out- some guys prefer that stance. The downfall is- that will change the behaviour of the loaded truck and negate the purpose of the rake.
Likely, a levelling kit up front and some bags in the rear to offset the extra perceived sag from pitching the nose up will be fine