The U.S. Postal Service says it’s ready for the holiday rush after recent upgrades, but the agency faces tough questions about its future on Capitol Hill.Lawmakers are concerned about how a major reform effort, including plans to consolidate facilities and collection routes as early as next year, could impact service for their constituents. The Postal Service says key investments in delivery centers and package sorting machines are helping them pick up the pace in its peak season. The growing focus on the package business is part of a broader system overhaul, branded as the “Delivering for America Plan.” The 10-year roadmap is aimed at fixing a long-standing problem.“The fundamental issue is USPS has an unsustainable business model,” said David Marroni, who has studied the agency’s operations for the Government Accountability Office. During a testy Senate Oversight Committee hearing last week, Postmaster General Louis DeJoy said mail volumes have plummeted over …