Could a new thermostat and spark plugs help a 2000 Mazda 626 that is overheating after driving 5 minutes and is not losing water and does not have much power?

it is hard to say without seeing the vehicle but check the coolant. make sure its not contaminated. (it should be nice bright green) if you replace the spark plugs make sure you replace them with plugs with the right heat range. also listen to the way your transmission is shifting make sure that is not slipping.