Your fans should have no effect at highway - Freeway speeds. The airflow through the radiator does the cooling. Make sure you have the OEM or Behr thermostat. The erzatz ones work O.K. but the washer/O-ring that comes with them is often suss. You can buy the correct O Ring at your local stealership for very little money.

Have you done a reverse flush on your radiator? Make sure there is no crud buildup between the radiator and the AC condenser. Make sure you have new radiator hoses. Any air leak will give you higher temperatures.

The M103 even with the AC on should have a lower temp than 100 degrees at highway speeds.
What temp does you car operate at freeway speeds without the AC?
If you turn the heater up does the temp come right down?