What was found
PRIOR TO DEPARTURE, APU AUTO-SHUTDOWN AT GATE. DURING CRUISE FLIGHT, THE RT GENERATOR DRIVE LIGHT ILLUMINATED, ALONG WITH THE EICAS MESSAGE. FOLLOWED THE QRH PROCEDURES, DISCONNECTED THE RT IDG DRIVE, AND DIVERTED THE FLIGHT. LANDED WITHOUT FURTHER INCIDENT. MX RAN APU, AND IT OPS CHECKED OK. THE RT IDG WAS REPLACED.