why is my monte overheating

acts like thermostat is sticking....so i put a new thermostat in and put hoses on, then i flushed the system. That didn't work so i put a new waterpump on...still doesn't work. i put a sending unit on and it still overheats!!!!today i just put another thermostat on just to make sure i didn't get a bad one. oh yeah, i "burped the radiator" which was suggested by a local guy and that didn't work. Please help...oh, sometimes when i would test drive it, it wouldn't overheat or if it did the gauge would go up a little past 3/4 and the jump down a little below 1/2 way.

P.S It held up to a preasure test and lost no coolant.

hey man your car might not realy be over heating it might just be that your guage is off. but the way it sounds is that when you replaced the thermostat you put a higher temp one in so it might be just reading a little high. to cheak it out warm your car up and then when it looks like it is to where it would overheat pop the cap off and stick a thermomiter in the fluid to see the actual temp of the antifreeze. after that cheak it against the size of thermostat you put in. i would run around a 185 degree.

Dont forget to check the heater core..
But also check the gauge. If you changed all that, then the next thing is a manifold gasket and you dont want to change that for nothing.
Oil can also cause a overheat.. Thats how a engine dies.