To put it simply, the speed limit is not a speed requirement. As a towing operator, you need to find the suitable speed for the conditions you find yourself in rather than simply attempt to match the speed limit of the roadway.
Some Factors to Consider While Determining Speed
The size of your truck.
The weight or size of the load.
Construction or road conditions.
Visability and weather.
Traffic
REMEMBER
Even if vehicles behind you are pressuring you to speed up, maintain a speed that you know is safe you are comfortable with.