Jim - LS engines are kind of notorious for air pockets in them, particularly in the rear of the heads. I would suggest you test your thermostat in some hot water on your stove and see if it was opening in the 185 to 190ish area. If so, depending on what you have available, either use a coolant filling system/tool or you can raise the front of your coupe so the radiator or fill tank is higher than the engine. Fill your system and if possible, once coolant is flowing through the return hose, massage the hose (full disclosure, forearm workout) to force any air out of the system. Let it run like this for a bit and the air pockets should work their way out of the fill tank.