If the Georgetown 370 is a 37 footer, yeah you are probably getting all the performance you are going to get from that V10 (and 4 speed transmission?) on steep grades. A Gear Vendors over/under drive might help.
And yes, there is usually a speed governor that will kick in around 80 mph. Your tires aren't rated for speeds over 75 and the handling & suspension aren't adequate for more either. Slow down a little and we will all be safer.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL