overheating maybe water pump?
2005 gto ls2 temp was spiking until got temp warning light and service oil light then car shut off had it towed to chevy they thought it was a blown head gasket but were not sure. It has always leaked coolant from the bottom of the reservoir when radiator is above 3/4 full. Replaced thermostat and radiator cap and still overheating especially at idle, when it's hot I cant even squeeze the lower hose by the thermostat. Could it be the water pump not producing enough pressure to open the thermostat?