bmw over heating?!?

hi guys,just had a problem with my 330xi i was driving normal speeds on the highway when all of a sudden my over heating red light came on,i stopped immediately ,and had my car towed,i did have a leak from the expansion tank.i replaced it but still is overheating.i then installed a new upper radiator hose,thermostat,water pump,oil thermostat and still overheating!the car doesnt have any leaks,so i:woot: have no idea what is causing the over heating

any info will help

thanks