Did you remove the lower radiator hose or open the valve on the radiator after you flushed it to drain the system? I'm sorry its really hard understanding what you mean, and yes it should hold 11.9 quarts when completely empty.
When you run the truck is the thermostat opening and pulling water through the system? You can verify this by watching the temp gauge and seeing it get over 200 and then drop back to around 190.