How do you replace the heater core on a 97 gmc Savannah van 305ci?

To replace the heater core on a 1997 GMC Savana van with a 305ci engine, start by disconnecting the battery and draining the coolant. Remove the dashboard and HVAC assembly to access the heater core, which is located behind the dashboard. Disconnect the heater core hoses from the engine bay, remove the old heater core, and install the new one. Finally, reassemble the dashboard, reconnect the hoses, refill the coolant, and reconnect the battery.