isn't the USPS already separate from the federal government?
It's a complicated situation. They are answerable to Congress on a lot of things, like if they want to raise the price of stamps and how much they pay for pensions. They are techinically an independent establishment of the Executive Branch of the United States Government. They run themselves like a business, however, not like a government agency.
As to whether to privatize, I support it. FedEX and UPS have proven that private companies are capable of providing service just as well as the post office.