The main problem with the USPS is that Congress has them operating as a semi-business, semi-public service.
That is to say, Congress has told them "act like a business, and turn a profit." But they won't let the Post Office do the most basic of business-like things: set prices.
They can't raise stamp prices, they have draconian rules imposed on them about pension funding, etc. Now, I'm not against Congress artificially keeping stamp prices low - we can view that as a public service similar to roads (we don't expect the Highway Department to turn a profit). But we need to pick one or the other - either is a "government business" and needs to run like one or a public service where we expect a loss for public good. Asking for both gets us dysfunction. It's amazing the USPS is as good as it is, all things considered.