I picked up my used 07 LD in Ca and drove it back to the Washington DC area a few years ago. It was my first trip in an RV though I had driven U-Haul trucks for family moving to FL and the like. After I was sure about the RV in an open stretch of road in AZ I put the peddle down and was surprised how quickly it moved up to the 90 MPH range. I quickly backed off the peddle and did an extended run staying with traffic driving from Phoenix for Tucson. Gas milage sucked. The rv felt good, with perhaps a little less road feel than my MINI.
After that I have never really run an extended run over 55-60. Even when crossing TX. Most of my long drives now are along the east coast. Some times in traffic I will go up to 65 so I do not clog those behind me. On I 95 traffic 20 MPH over the 65- 70 MPH speed limit. I just keep to the double nickel and stay to the right when that happens. I would not be able to keep up any way and they can see me a long way back. There are plenty of trucks going the same speed (or slower).