Susan Muffley Act of 202 3 This bill restores the full vested monthly benefits for eligible participants of certain pension plans that were sponsored by Delphi Corporation and terminated as a result of General Motors' bankruptcy in 2009. The Pension Benefit Guaranty Corporation (PBGC) must recalculate and adjust each plan participant's monthly benefits payment. The PBGC must also apply the recalculation to previously-made monthly payments and make a lump-sum payment for any additional benefits based on the recalculation. The bill establishes and provides appropriations to a fund for the payment of these benefits and specifies how the lump-sum payments are treated for tax purposes.