I just did a Google maps route:
1521 miles - Kansas City, MO to Sioux Falls at I-29/I-90 to West Glacier
1437 miles - Kansas City, MO to Sioux Falls to Fargo to I-94 to West Glacier
Not only is it only 84 mi. farther taking I-94, it will also be the fastest.
From I-94 you can check out Theodore Roosevelt Nat'l Park. Weave yourself up on Hwy 13 to Hwy 2, taking Hwy 2 to West Glacier. You won't have to get on I-90.
Full-timed for 16 Years . . .
Traveled 8 yr in a 2004 Newmar Dutch Star 40' Diesel
& 8 yr in a 33' Travel Supreme 5th wheel