Advice please - Edmonton to Phoenix in January

Harvard wrote:
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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. ....

I'm surprised that you would consider I90 north of Butte to be steep, but aren't bothered by the Lost Trail pass on US93. There's a ski area at the top.

When I took US93 from Salmon to Missoula, I encounters snow flurries in easly June. But the soak at the hot springs on the north side of the pass was quite nice.