Part Type: HVAC Heater Core. Aluminum Heater Core. Heater Core. 2007 GMC Sierra 3500 Classic Submodel: Crew Cab Pickup; Engine: 6.0L V8; RPO Code D07; w/ Rear Vents In Center Console;. 2007 GMC Sierra 3500 Classic Submodel: Crew Cab Pickup; Engine: 6.6L V8; RPO Code D07; w/ Rear Vents In Center Console;.