engine still not cool enough

If it still run HOT while crusing with a 50mph wind hitting the rad, you need to play close attention to the air flow getting to the rad.

Do you have a multi meter, one with a thermocouple hookup? Try putting a probe in different areas of the rad and see if there are any cool spots. Make a grid and do it one square at a time. Maybe you have a restriction some where.

And yes, if you have a restrictive exhaust, it will make an engine run hot.