We have taken this trip every Dec 27/28/29 for the last 12 years.
There are a lot of steep terrain on I15 between Great Falls and Butte. We always take HWY 93 to Missoula then either I90 on to Butte or Hwy 93 to Salmon. From Butte you have the choice of I15 to Las Vegas OR rejoin Hwy 93 at Twin Falls, ID (Dubois and Hwy 22 to Arco). If you take Hwy 93 in Nevada DO NOT take Hwy 93 between Ely and Ash Springs. Instead take Hwy 6 out of Ely then Hwy 318 to Ash Springs, it is 40 miles shorter and a very good 70MPH highway.
Do not take Hwy 93 between Salmon and Arco in Idaho, it is slow and takes every twist in the Salmon River.... If you are going to do Hwy 93 to Salmon then take Hwy 28 out of Salmon to join Hwy 22 then on to Arco.
