I just ran U.S. 89 from Livingston to Browning a month ago. Most of it was high plains but between White Sulphur Springs and Monarch you drop down into a beautiful valley for a number of miles. There was a stretch of about 5 mi that was under construction and the drop into the valley and the climb out are long grades. What are you pulling and with what? I was pulling a 38' car trailer that weighed in at about 6800 at the time pulling with an 07 GMC CC dually LBZ Duramax. None of the route put a strain on things