Infighting between the boards of bailed-out finance company GMAC and its struggling mortgage unit Residential Capital is jeopardizing GMAC's plan to sell the money-losing lending ship, sources tell The Post. According to people familiar with the matter, GMAC's and ResCap's boards are fighting over how to sell ResCap, a money-losing home lender that nearly collapsed, and brought GMAC with it, due to its underwriting of subprime mortgages. While GMAC has assumed control of the sale process, sources said officials at ResCap are keen to determine their own fate, and may hire their own investment bankers to handle the sale. Because of the way ResCap's relationship with GMAC is structured, both sets of directors must participate in deciding what to do with ResCap.