Does your car run hotter at higher speeds?

Any engine will run warmer with it working harder.

But...
- scaled-up radiator
- retarded timing
- lean mixture
- blocked airflow (large transmission coooler fi)

These are the things that can/will increase engine operating temps by itself.

My own '73 Dart has an old scaledup radiator and it causes engine temps to start rising above 195-200deg. above 70mph.
Below that it can drive or idle all day in 80deg heat.