If it over heats more with it idleing I would suspect rad. pluged with bugs, try to see if you can put a trouble light on one side of the rad. and look through the other side and see light through it. If rad was pluged inside it would overheat quicker driving down the road. The best way i have found to see if head gasket is blown is to remove the thermostat, remove the water pump belt. fill the cooling system as full as you can with stat removed and housing installed. start the eng and look for bubbles in where the stat should be. You will get a few bubbles at first due to trapped air pockets but if it looks like you are blowing into a straw in a glass of water you have a problem. If it all looks good then put a new stat in when you put it back together.