Most maps in this part of the states show national forests (and parks) in a distinct color. In the West, forests are on the mountains, the valleys between are drier, and owned by ranches or BLM. So if the route does not cross a National Forest it is unlikely to have significant grades. River crossings may have a grade as well, but probably not as long.
Turn on 'terrain' mode and you'll get an even clearer of sense of the layout.
Zoom in some more and you'll see that US26 is relatively flat and straight.
US20 enters a canyon north of Shoshoni (Wind River Canyon). Roads that follow rivers have curves, but usually no major grades. North of Thermopolis US20 crosses open ground, where wind will be more of an issue than curves or grades.
Looking a little closer I see there's a cut and grade where 20 climbs out the Big Horn River south of Thermopolis. In streetview that shows a generous climbing lane.
In Sat view I can see a tunnel just north of Boysen St Park in the Canyon. In streetview there's a sign that warns of 3 tunnels ahead. They are short. No height warnings on the rocky entrances. The Streetview car passes a large 5th wheeler (Jayco Pinacle) just north of the tunnels. And a 14' clearance sign.
A railroad passes through the same canyon, on the other side of the river. Trains don't like grades or sharp curves.