staying to hot /overheating

My problem is that i have replaced the headgasket with the oem gasket and i have replaced the raditor with the 4 core raditor the is the only you can buy now for the car and i have replaced all the hoses and the waterpump as well as the thermostat and i had to run a direct switch for the fan i have barely no heat and i put the suggested amount of antifreeze in the car which is one galon of antifreeze which is the pure stuff not the 50 50 stuff and filled the rest up with water i am not leaking any water that i can see except right before the back of the engin compartment is this device that has some heater hoses conected to it and looks like a vacum with some kind of switch on it leaks a very little after runnin it all day i can not figure out what it is or how to replace it and i can not find it in a haynes book anywhere so if some one can help me to determine what is wrong and /or tell me what this thing is i would like to figure it out..Plus i have checked the heater core and it looks like it is not leaking from anywhere as well so i figure it is o.k. please tell me that i am right ...thanks

have you had the cooling system flushed? sounds like its clogged up somewhere.