I need some help solving an overheating problem. It has a fresh rebuild 390, bran new Edelbrock waterpump, 3 year old rad, factory cooling fan with a dealer installed fan shroud for A/C cars. The car overheats in about 5-10 minutes. seems like the thermostat was not opening, bleed the system at the upper heater hose so I do not think we had any air in the system. Removed the thermostat & it still overheats, just takes longer. We were thinking is we had an air lock at the thermostat & without the t-stat the coolant was flowing to quickly to cool down in the radiator. I drove the car about 8 miles without the t-stat & while driving the temp. was stable but went up everytime I stopped for a traffic light & the temperature would not come back down when driving. Installed another t-stat, this time with a 3/8 hole drilled through it at the top to release any air trapped behind the t-stat. Overheated more slowly just like it did without the t-stat. Was now thinking had one ore both of the headgaskets install backwards blocking the rear coolant passages. removed heads to find the gaskets had been installed correctly. Timing has been checked & rechecked, & if anything it is running a little rich not lean. We are pulling our hair out & any help from you FE guys would really help.