2000 Dodge Neon overheating

Air pocket ? You did have it all opened up , do the fans come on when it gets hot ?

Consuming water means it is still leaking internally. Maybe the head was warped, you didn't mention you have it machined before replacing the gasket. Like chevy stated, did you bleed the system? How is the radiator, you didn't say you replaced that? A car overheating with the AC on usually indicates an AC compressor issue. I personally think you should have not gone the rabbit hole of putting money into this vehicle. Neons on a good day were not very good reliable vehicles.

Is it consuming water or boiling over? You didn't say you replaced the radiator. It could be clogged and leaking. The heater core could be leaking. Did you replace the timing belt? Is the valve timing set correctly? Is the check engine light on? If it is are you getting a knock sensor code? If you are the ignition timing could be severely retarded. Does the engine have a valve tap? A valve tap can trigger the knock sensor and the ignition timing will be severely retarded. Does the engine lack power? Another symptom of retarded ignition or valve timing. Is the cylinder head aluminum? If it is, it was done (warped) the very first time the engine overheated. Are you seeing lots of white "smoke" from the tailpipe? This will be water condensation from the warped head. Did you torque the head correctly and use the correct tightening sequence? Did you check the lower radiator hose for collapsing? A weak hose will sometimes collapse from the suction of the water pump and restrict the flow of coolant. Does the engine overheat when idling, like waiting at the bank drive through? Or when you're driving? It makes a difference. Hope that helps! Jim