What was found
FMC- ACTED VERY SLOWLY, TAKING UP TO 30 SEC TO COMPUTE A NEW ROUTE, DID NOT DISPLAY ETA FOR ACTIVE WAY POINT ON NAV DU, DISPLAYED NO ETA OR FUEL COMPUTATIONS ON PROGRESS PAGE. ENROUTE WE EXPERIENCE VNAV DISCONNECT. ACFT GROUNDED. REPLACED NR 1 FMC COMPUTER REF MM 34-61-02, GROUND VERIFICATION TESTS GOOD. FMC SELECTOR SWITCH MOVED TO NORMAL CONFIGURATION.