need help on a overheating problem

i have a 94 cavalier that overheats while driving, but doesn't while just idling have changed thermosate and redid the head and gaskets. here is the thing it did the same thing before i blew the head gasket so i m stumped have heard bout having an air bubble in the cooling system but ran it without the raditor cap and watched it circulate so i know the raditor is working please help