Had similar problems with my P6P. There are multiple areas in my town where I show full / nearly full bars, but my service is terrible or non-existent (!). If I toggle Airplane Mode, I’ll get great speeds until it drops out again. Sometimes this is 30 seconds, sometimes 30 minutes, sometimes hours/days. But at some point it will drop out again. Ugh…
I’ve had that problem too. And way too much congestion in an industrial area during lunch and breaks.
So I went to another carrier.