2001 Mitsubishi Galant ES V6 has an overheating problem, replaced Thermostat, checked for cracked Head gasket and it's not either of those things, what else can I do, if I change out the water pump an

compression test cyclinder may have cracked head or warped head .I think that car has an Astron motor from my memory which has an alloy head that can warp or crack if the engine has been overheated ?

If its a shake it may be a head gasket that is out. Did the cars radiator get hot ? Check the radiator and dipstick for signs of oil. The dipstick will be milky. You can usually smell oil in the radiator.

there is a metal tube that is your upper redaitor hose that runs between the cylinders under the intake manifold that have a thin rubber band gasket on each side . they are common to go bad.

have the cooling fan system checked
check the heater core
possibly thermostat
could be an improperly replaced head gasket, if head was a used head it could now be cracked

there are about 40 things that could cause your problem, and can only be properly diagnosed by a trained mechanic with the proper tools

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

a few things to check before we condemn it as a leaking head gasket(pressurising water out).
First check the radiator cap seal,no cracks and that it takes some pressure to push the spring loaded part down.
Does both the top and lower radiator hose get hot as temp gets to normal(where thermostat should be open).if not,the thermostat may be a faulty one or has slipped out of seat as the cover was bolted back down onto it.(temperature will differ either side of it).I have had some of these come in with part of the waterpump impellor rotted away.same symptom of one hot and one cold hose,and water doesnt flow inside radiator with cap off(ensure this is not removed if engine is hot)and temp where the thermo should be open.
Possibly the radiator needs sending out for the top or side tank to be removed and each tube cleaned out.this is a lot more effective than trying to reverse flush with water only.
But if temp is normal these areas should be fine.
Do the hoses swell with pressure and become hard to squeeze in a short time?this could reveal a leaking head gasket and should be tested with a teekay type tester for the presence of cylinder gases in cooling system.
Do the fan(s) come on if sitting idling at normal temp for 5-10mins?water can be pushed out if they dont come on or their cut in/out temp is incorrect.hope this helps.
let me know some times re when it pushes water out,do you hear a boiling sound from inside engine or radiator when this happens,any other info that may help diagnose.

the engine is leaking coolant internally, via either a bad head gasket, cracked cylinder head, or cracked block.

I would go with slowcalafl. It is either air, or a cracked head bad head gasket. Remove the radiator cap when cool. Start up the car and watch for bubble emerging from the coolant. If it continues to bubble, you have a bad head or head gasket. If not, look for improper timing as another possibility.

look for weak valve springs.

It could be head gasket, the water could be leaking into the cylinder/s. Is there excessive steam coming out of the exhaust?