I just replaced the head gasket but it still over heats.

I wouldnt unless you want to spend money and possibly not fix your problem if you just replaced the head gasket or gaskets did you bleed all the air out of the cooling system first? and second what caused your car to overheat in the first place and caused it to blow a gasket? also did you have the head checked to see if it was warped? and for cracks that you cant see aluminum heads have to be pressurized with water to find cracks and if the head is warped but still can be shaved so your new head gasket will seal and not leak between cylinders which can cause it to overheat. i could go on and on with more possibilities to why your car still over heats. first bleed all the air out of the cooling systems alot of cars engines have bleeder screws on top or near the thermostat housing if it does crack it open and with it running air bubbles or steam will come out keep adding water until you have a steady stream of water coming out of the hole of the bleeder screw then tighten it once you see no more air is present alot of the time that will fix your problem provided your head isnt warped or have a crack and your radiator is flowing to spec and your thermostat is working correctly. Just trying to help good luck.

Research > combustion leak test..