I can certainly vouch for the performance of KTNN not matching the 'predicted coverage'. Over the years I've been through the Navajo lands and around them a few times and while it does manage to serve the entire nation during the day, it isn't as robust and one might think.
I find the station (and the Navajo and Hopi cultures) to be rather fascinating and would love to get back out there and do some real exploring there. It's really a whole other world in some places. There are now a smattering of FMs here and there, I think one belongs to the Hopis (whose land is all inside the Navajo Nation, but a separate nation unto itself I believe) but none of them come close to covering everything from Tuba City to Window Rock. And I don't think any of the FMs do full time Navajo-geared programming, either.
Also, KTNN ran C-Quam stereo at one point, but I don't think it's on anymore, either. I tried it and a station in Gallup, NM that was on the AM stereo list and neither came through. The caveat being the radio itself might be dysfunctional, though. I can't find a strong local stereo signal to verify it with and WLS at night is usually buried under Cubans where I live.