The differences between stock and custom pickup trucks is that custom trucks have had additional aftermarket modifications substituted for or added onto the standard equipment that comes with the trucks. Truck customizations range from cosmetic alterations that do not affect vehicle performance to extensive mechanical modifications that alter and replace large portions of the vehicle's engine, drivetrain and suspension systems.
Many common modifications made to custom trucks are cosmetic in nature, including specialized exterior lighting systems, decals and custom body panels. These alterations can also be functional in nature, such as lighting arrays on the top of trucks that are used to provide more light than the standard headlamps or the installation of large custom wheels and larger tires for better traction in mud and snow. Interior cosmetic customizations are also common, including custom graphics on a truck's instrument cluster or modifications to the steering wheel.
Performance modifications on custom trucks can involve augmenting the existing mechanical systems of the truck, such as when owners install a high-flow exhaust system to their custom truck to improve its engine's power output. More-extensive performance modifications may completely replace the entire original system of the vehicle. One example of this sort of modification is the replacement of a truck's factory suspension with an off-road suspension and solid axle in many custom trucks meant for off-road use.