First job is to determine why it’s overheating. Other possibilities are plugged radiator, blocked hose, or leaking head gasket. Check the head gasket first before you start replacing parts. With the engine cold, remove radiator cap and start the engine. Have someone rev the engine while you look for bubbles in the coolant. Bubbles = head gasket leak. You can also secure a plastic bag over the filler neck with a rubber band, squeeze closed the overflow hose with vise grips, and see if the bag inflates. Or you can do a more scientific test and have a mechanic use a chemical test kit on the coolant to determine presence of mildly acidic CO2 from a head gasket leak in the coolant. You can also buy a test kit and do it yourself.
The low power/running poorly also suggests low compression from a blown head gasket. You can have a mechanic do a compression test on the cylinders and a leakdown test on the cooling system.
If you can verify that the head gasket is not leaking, then you can investigate the other options. But with that many miles on the engine, you may not be that lucky.
Here’s some forum info on head gasket replacement. Apparently it’s not hard for a home mechanic on this car:
And apparently these engines can blow a gasket between cylinders without leaking coolant. So even if the cooling system is intact, the gasket may be leaking between cylinders. Again, have a mechanic do a compression test on all cylinders.