temp goes up when idleing too long in neuteral

My 93 grand am used to get real hot when sitting and idleing for too long then it got really hot on the highway and blew the head gasket and wrecked my head so i replaced the engine with a new 3.3. I thoght everything was better but now its still doing it!!!! What could it be please help. it is full of rad fluid and no antifreeze in oil.

It sounds like the cooling fans are not coming on and moveing air through the radiator when you are sitting still. The other issue is that if the air dam on the bottom of the car is missing it can cause a loss of air flow while on the highway and cause overheating. Finally, you may want to make sure that the radiator is not internally blocked. Sometimes corrosion will cause a partial blockage and then the car will overheat.