That is on the high side. We've never had it on our Alero go one needle mark above the half mark on the gauge even with A/C off. But our LIM gaskets were replaced with the revised GM ones about 3 years ago.
Also, be sure to carefully inspect the area of the cylinder head and LIM at the thermostat area. Some members had leaking via the LIM bolts and even a cracked LIM. The thermostat could be the issue so it would not hurt replacing it although it is a PITA to replace. At least cure the external leak since a loss of pressurization in the cooling system will cause the engine temperature to rise.
On LIM gasket symptoms it varies. You can have engine oil and combustion by-products in the cooling system (looks like sludge), coolant in the crankcase, an external leak only or just a simple unexplained loss of coolant via the intake system and being burned in combustion.