* Third-generation (or Gen 3): This refers to the specific model year range and design iteration of a particular truck *model*. For example, the Ford F-150 has had multiple generations. "Third-generation" denotes a specific period in that model's history.
* Crew Cab Chassis: This describes the *cab* and *body style* of a truck. "Crew Cab" means it has four full-size doors and seating for at least four to six passengers. "Chassis Cab" means it has a bare frame without a factory-installed bed; the body is customized or a specialized body is added by a third party (think dump truck, flatbed, etc.).
A truck *could* be both a third-generation model *and* a crew cab chassis. But those are two independent classifications.
