B757-200 FLT CREW EXPERIENCES TRAILING EDGE FLAP DISAGREEMENT EICAS WARNING ON APCH TO ZZZZ. WHILE DIVERTING TO ZZZZ1; CREW FAILS TO RESET ALTIMETERS.

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ON THE APCH TO ZZZZ; OUR FLAPS STOPPED DEPLOYING AT APPROX 17 DEGS; AND THE TRAILING EDGE LIGHT ILLUMINATED. WE ACCOMPLISHED THE MISSED APCH PROC; AND CLBED TO FL200 AND ENTERED HOLDING OVER THE VOR. AFTER REVIEWING THE PROC FOR THE FLAP MALFUNCTION; WE DECIDED TO DIVERT TO ZZZZ1 BECAUSE THE PROC STATED TO LAND WITH FLAPS 20 DEGS. WE DECIDED THAT AFTER DISCUSSING LNDG AT A HIGH ALT ARPT WITH A FLT CTL MALFUNCTION; WITHOUT ANY LNDG PERFORMANCE INFO; AND THE FACT THAT THE RWY WAS RPTED AS WET. OUR DECISIONS HAD TO BE MADE QUICKLY DUE TO THE NATURE OF THE EMER AND OUR FUEL STATE. WE KNEW THAT WE WOULD HAVE TO FLY A LONGER RTE THAN NORMAL TO ZZZZ1. BECAUSE OF OUR FLAP PROB; WE WERE LIMITED TO FL200 AND WE NEEDED A RTE THAT HAD AN MEA BELOW THAT. WE ALSO KNEW THAT OUR FUEL BURN WOULD BE HIGHER THAN NORMAL DUE TO THE FLAPS BEING PARTIALLY DEPLOYED AND THE LOWER CRUISING ALT. AFTER WE WERE ON OUR WAY TO ZZZZ1; WE NOTICED THAT WE HAD NOT CHANGED OUR ALTIMETER SETTINGS TO 29.92; AND WE THEN RESET OUR ALTIMETERS AND LANDED IN ZZZZ1 UNEVENTFULLY. THE WORKLOAD FROM THE BEGINNING OF THIS INCIDENT UNTIL WE LANDED WAS EXTREMELY HIGH. THERE WERE MANY FACTORS TO BE CONSIDERED; AND THE COMBINATION OF VERY LIMITED COMS; THE WX IN ZZZZ AND ZZZZ1; THE MOUNTAINOUS TERRAIN; THE ACFT MALFUNCTION; THE DIVERSION; AND FATIGUE MADE FOR A VERY CHALLENGING SIT. WE SIMPLY FORGOT TO RESET OUR ALTIMETERS CLBING THROUGH FL180 AND DID NOT ACCOMPLISH THE AFTER TKOF/CLB CHKLIST UNTIL WE WERE ON OUR WAY TO ZZZZ1. SUPPLEMENTAL INFO FROM ACN 675146: WE FOUND A RTE THAT HAD AN MEA OF FL190; THE LOWEST FOR OUR ROUTING. WHILE FLYING THE RTE; WE BROKE OUT ON TOP OF THE CLOUDS. APPROX 15 MINS ALONG THE RTE; CTR QUERIED US ON OUR ALT AS THEY WERE SHOWING US AT FL194.