I have a 87 7m-gte whith a new oem radiator, radiator hose, and thermostat. I just did a system flush but in the city i NEVER have a heating problem no matter how hard i drive it , but at highway speeds at 3000rpm in 5th gear i start to over heat.I think its because im missing the front air defuser that guilds air into the intercoller and radiator. any suggestions?