Finally found the problem…
Settings,
Wireless & Networks,
Mobile Networks,
Automatic Connections,
Uncheck Sprint Connections Optimizer.
Thank you to the Sprint Store Rep who showed me that!
F-U to the POS “Customer Care” rep who insisted that “it’s nothing Sprint did”.
I’m no genius but I’m smart enough to know that ONLY SPRINT cares what network I’m using to stream TuneIn!