As I've said before, the Postal Service works in mysterious ways. Very mysterious. They sell Prority Mail as a 2 to 3 day service. Out of four packages sent Priority Mail this month, one to Chicago took 8 days; One to New York City took 7; one to Denver took 5 days (Denver is only 100 miles away) and one to California took 3 days. So, only one in four packages arrived on time. Of course "It's not guaranteed." Boy, that's for sure. If they guaranteed it they'd go broke. Wait, they're broke anyway. Thanks to the wonders of delivery confirmation, it removes all doubt of what a crummy job they do.
Even though it costs more, I send more and more stuff UPS. The three packages I sent UPS all arrived on time.