T-Mo's connectivity should get better along that drive and in your area, and pretty soon. I don't recall exactly when (I think it was May or June last year), TDS announced an interop agreement with a few carriers, including T-Mo. TDS (Telephone & Data Systems) owns/operates U.S. Cellular, TDS Telecom, and a few other rural providers; I heard about it last year when a friend in my region passed it on - she gets service from BendBroadband, they're owned by TDS. My point here is that the TDS LTE Band 12 interop with T-Mo and a few other cell providers is set to start Q1 2017. I'm pretty sure that the ATTWS roaming agreement has kicked in as two of my employees are on T-Mo and their phones started working a couple of months ago in areas in Oregon where there was no prior service but I know that ATTWS was working there (I carry one ATTWS and one VZW iPhone).The part about T-Mobile that has me wary is that we do like to drive to Chicago to see family, and Iowa is full of dead spots along I-35, and service even in Chi-town can get spotty (granted the last time we were there my fiancé was using a ported over AT&T 4S). Although Verizon went completely dead in the Ozarks when we drove through last summer while T-Mobile roamed onto AT&T.
With ATTWS turning off 2G a couple of weeks ago some of my mom's friends with ATTWS in Skamokawa (literally on the edge of cell reception) who had no service inside a month ago are getting excellent reception now. One of them, a B&B owner was telling me over lunch last week that he doesn't need to go outside to make a call. I might just snag a T-Mo test drive phone or SIM to put in a 6S+ and see what's what…
I'm still locked into my VZW contract with UL data, but it's working well for me so far. Still happily beating up VZW's network, since 2011! Cheers!