Considering that neither Colorado nor Nebraska have a state highway numbered 38, US 38 should be resurrected. It can be done this way: From the corner of 9th and O Streets in Lincoln, US 38 can go westward on US 6 and US 34 to west of Fort Morgan, CO. Westward from there, US 38 can piggyback onto I-76 and I-70 to Exit 232, then take over current US 40 all the way to I-80 at Park City (UT).
Now, there may have to be some changes. For example, US 34 would have to end at Grand Island, leaving the standalone section of US 34 between I-76 Exit 66 and Granby to be SH 34. Also, US 6 would have to piggybacked onto I-80, I-76, and I-70 between Council Bluffs and Loveland Pass (CO). Not to mention, UDOT would have to renumber SR 38 north of Brigham City. But still, this renumbered US 38 would be an excellent fit to the grid between I-80 and I-70.