For most of the '80s and 90s, I made the run down I-44 from St. Louis to Joplin 2-3 times a year. Sometimes extending south into northwest Arkansas or west to Wichita.
The Radio-Locator maps are pretty much in line with what I remember. On a car radio, I typically had a good signal from roughly Rolla to Joplin. Going south from Springfield on US 65, the signal was steady for about a half hour into Arkansas. During most of that time, "The Gentle Giant" was basically beautiful music instrumentals.