i have a 2003 wrx with AP stage 2 downpipe uppipe bola 3inch cobb intake. i was driving the car home from a shoot out an i went to the gas station shut it off and it blew a ton of white smoke. check the codes said it was missfireing. i replaced the plugs codes went away. then it went away. then im driving home the car overheats. i take it to my garge pressure test for head gasket it passes the pressure test. i let the car idle for about 20 mins dose not over heat i take the car around the block build boost then it over heats. i shut off the car then start it still warm blows white smoke when its cold it dose not blow white smoke. i think its the head gasket but im looking at the heads and there is not even dirt on them they look brand new. im totally lost i need help ASAP.