According to what I see on Sprint’s map, coverage along I-80 with the exception of metro Cheyenne is roaming. In theory, you should have talk & text but no data coverage. Roaming is, of course, best effort, so theory and reality may well differ, at least, in part.
For the most part, T-Mobile’s map does show native rather than roaming coverage along I-80, however, much of it is characterized as “fair” signal strength. Here’s how T-Mobile describes “fair” “Cell coverage outdoors and occasionally indoors”. Consider a moving vehicle to be “indoors”.
Well, there’s nothing to lose, I suppose. You might you a GSM (T-Mobile network) SIM for one phone while leaving the other on CDMA (Sprint network) to maximize coverage options.
While the merger is complete, for the most part, the networks remain separate. I’ve seen one report in Community from @billg indicating his (I believe) GSM SIM is using what are or were Sprint towers. It’s possible in some areas, T-Mobile has refarmed some Sprint coverage to the T-Mobile network. Generally, to date, where this is done it’s being done for 5G, which your Moto G5 Plus is incapable of using. Depending upon the flavor of 5G deployed, if any, you might have improved coverage on Republic with a 5G phone. For more on that, please see here: Understanding Emerging 5G Technologies.