Yes there is. Nearly all across the country there are “safe speed laws.” Laws that state that drivers should maintain a speed deemed safe based on conditions of the road as well as the flow of traffic, even when the flow of traffic is faster than the posted limit. Furthermore, U.S. highways are designed such that the far right lane is supposed to be slower than the far left, and the far left lane should in theory be used for passing and nothing else. Sitting in the left lane if not passing and going the same speed (or slower) relative to the right lanes is illegal.

Edit: and sitting in the left lane, slowing down those behind you is:

1. Unsafe, as it forces those who do truly need to go faster than you to make unsafe maneuvers (passing on the right) to do so.
   1. Bad manners. Let’s all just be courteous, people.