i have a gemi radiator in mine, and an intercooler in front of it, i also have the cooler thermostat in (around 76 degrees instead of 86 or something), it holds beautifully on the cooler temp, well below half on the guage, until i stop in traffic or at lights where it heats up like crazy, i also have a shroud on the radiator (its not an ideal shroud but better than nothing)

any clues on what is causing this?