What was found
MAP FLAGS ON F/O SIDE. UNABLE TO RESYNC FMC RT FMC FAILED. ACFT GROUNDED. WHILE ON DEFERRAL, PILOTS NOTED INPUT TO LT FMC VERY SLOW ON GROUND & INFLIGHT AFTER DEPARTURE. MAGENTA TRACK LINE DISAPPEARED, TERRAIN STILL AVAILABLE. REPLACED RT FLIGHT MANAGEMENT COMPUTER, OPS TEST IAW AMM 34-61-00-701-801, TESTS GOOD. OPS CHECK NORMAL, ACCOMPLISHED ON BOTH FMCS.