I've read through so many posts on overheating issues and have no idea where to start looking for my solution. Here's what I have going- my 2007 4.7 begins to overheat ie. gives check gauges warning signal while driving on surface streets. If I dump heat by turning on heater, temp gauge drops to just above mid point on gauge. This occurs regardless of outside temperature. When driving on highway, the temp stays just above normal without heater being turned on. I have checked the fan clutch by rotating when off as well as trying to slow while it's running. I have coolant at appropriate level and mix. When I touch radiator cap after driving, the system is under pressure, but the cap is not hot. I also noticed the top half of radiator is not hot. I'm not sure where to start trying to fix this thing. Any help is greatly appreciated.