I can see both sides of the issue here. You can actually get a ticket for not going a safe and reasonable speed relative to traffic conditions such as snow and ice, etc., regardless of what the speed limit is. A feeder driver pulling doubles would be wise to slow things down a little bit in many situations . In my opinion, the time needed to react to situations such as a car flying over three lanes to an exit, is more than when pulling a single trailer.
Now from the other side:, did this driver consistently go 58 in a 65 mph zone regardless of traffic conditions and weather? Was his cruise control set at this speed all the time? Did he do it consistently on repeated trips, regardless if he was the only driver on a well lit road on a rain and snow free night or if he was in some traffic with somewhat adverse weather conditions? If "yes" to the last two questions, then there is an issue here.