What was found
WHILE FLYING AT FL380 .78 MACH 245 IAS AUTOPILOT CMD 'B' SELECTED. AUTOTHROTTLE ARMED. THE MCP IAW MACH WINDOW SHOWED UNDERSPEED LIMITING SYMBOL (FLASHING A). AUTO THROTTLES ADVANCED TO INCREASE AIRCRAFT SPEED TO M.81; FMC CRUISE SPEED STILL SET AT .78. COMMAND A SELECTED AND MCP WINDOW CLOSED. AIRCRAFT RESUMES M.78 BOTH CA & FO AIRSPEEDS MATCHED. PERFORMED FIM TASK, PER FIM 22-11 TASK 826. R & R 'B' FCC, PER AMM 22-11-33, NO FAULTS NOTED. AIRCRAFT RECERTIFIED TO CAT III STATIS, PER MT 734-00-03 VERIFICATION NR 20738 RAR 83561 POS 2 P/N OFF/ON 822-1604-101 S/N OFF 16D4GD S/N ON 1G0XY.