Since it doesn't overheat at faster speeds, that tells me the cooling fan isn't working properly. When driving, air can flow through the radiator to cool the engine. However, when stopped, there is no air flow. That is when the fan has to come on to draw air through the radiator.
Check that and let me know what you find. See if the cooling fans are working when it starts getting hot. (I believe in 05 they used electric fans. If it is a clutch fan, let me know.)
Heres an article on checking the head gasket, it will help
Monday, August 18th, 2014 AT 6:42 PM