Go to a modern well funded post office some time. They're incredibly efficient.
perhaps you live on a different world as I, but "efficient" businesses do not lose 1.9B USD every three months.
unfortunately, history has shown for at least 2500 hundred years that government bureaucracies always devolve into political quagmires, where empire building and ass-kissing trump sound business practices.
If you had actually bothered to read the article you linked to, you would have noticed that Congress is preventing them from taking cost savings measures the USPS wishes to implement. Congress controls the prices they can charge. Congress mandates six day deliveries. Congress prevents them instituting their own health insurance plan (which an organization the size of the USPS can easily do). Congress mandates pre-paying health and pension benefits many decades into the future (the only case of this occurring in the U.S. government, and also all but unknown in the private sector).
And then there all the Constitutionally-derived mandates for keeping unprofitable rural branch offices open, and delivering mail to every household everywhere, every mail-day. Things no private business will do.
When Congress's package of restrictions and controls essentially requires an organization to run a deficit, efficiency alone cannot turn the situation around.