Chevrolet: 2000 CHEVY IMPALA OVER HEATING???, chevy impala, radiator cap

Question
I'VE HAD THIS CHEVY FOR 3 YEARS NOW. ABOUT A YEAR AGO IT STARTED TO OVERHEAT ONLY IN THE HIGHWAY OVER 60MPH. EVER SINCE THEN I CHANGED THE WATER PUMP, THERMOSTAT, RADIATOR, RADIATOR CAP AND RECENTLY TWO BRAND NEW FANS. ITS STILL DOING THE SAME THING. IT OVER HEATS OVER 60MPH ON THE HIGHWAY. WHAT ELSE MAY IT BE?

Answer
IVAN hea- well i would have a rad. pressure test done to see if you have a leak some place, also is the belt slipping, or is the belt close enough to the rad. also is there a schroud on it.and if you have a large round hose on top of the rad. at times they will suck themselves closed and you would never know it. that will cause it to over heat, also a bad rad, cap. are the sensors for the fans working right. if you wish to try it, you can go with a cooler thermastat. or if you live in a warm area you can take it out alltogether and see how that does it. ok