Any government entity not subject to the laws of basic economics will grow less efficient, less effective, and more problematic over time. Market forces prevent this from happening in the private sector. If one company starts to charge to much or screw up too often, people will move to another company's services.
I shipped a package out last Friday from our local PO and it arrived at it's destination on Monday, but that was only a 150 mile trip. I've only had issues one time with USPS when buying something on the 'Fire - took my check several weeks to get to it's destination.