On US 26/287 you'll go over Togwotee Pass between Dubois and Moran Junction, WY. Not an issue, it's been greatly improved over the past 10 years or so. US 287 goes north through Yellowstone and into Montana at West Yellowstone, if you us US 26 through Jackson, Hobart Junction and Palisades Reservoir it's curvy but not any great mountains to climb. Don't use Teton Pass (WY 22) between Jackson and Driggs, ID, it's a 10% grade up and down and while beautiful, it's tough on engine, transmission, and brakes.
I don't understand your comment on gas stations, plenty of places to fill up during the day, many places close at dark in the area, but it's never been an issue in the 25 years I've been traveling the region.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI