I have a 2.2 with a new head gasket, rebuilt head, water pump. The issue is that the engine runs hot with my new and old thermostat. The antifreeze is cool be but engine hot, it seems like was it restricted. Here's the kicker when I remove.the thermostat it run just.fine what can cause the problem

 

you have a blockage somewhere. coolant only runs through the thermostat one way (like a check valve) so when you remove it the coolant is allowed to flow backwards through the engine which is why your not overheating without one.