B757-200 CREW HAD AN ENG THAT WOULD NOT PRODUCE RATED THRUST INFLT AT FL350.

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DIVERTED TO DFW DUE TO REDUCED PWR ON R ENG. DURING ENRTE CLB FROM FL350 TO FL390; THE ACFT STOPPED CLBING AT FL356 AND AIRSPD BEGAN DECAYING. AT THIS TIME; THE R ENG EPR WAS NOTED PEGGED AT MAX; WHILE ALL OTHER ENG INSTS WERE READING LOW. NO EICAS MESSAGES WERE EVER RECEIVED. WE REQUESTED AND RECEIVED FL350 WHERE WE COULD MAINTAIN APPROX .74 MACH. AFTER REVIEWING THE QRH AND FINDING NOTHING MATCHING OUR INDICATIONS; IT WAS SUGGESTED WE MIGHT RETARD THE R THROTTLE AND TURN OFF THE R ENG ELECTRONIC CTL TO SEE IF WE WOULD REGAIN FULL PWR. HOWEVER; PRIOR TO TROUBLESHOOTING THE PROB OURSELVES; THE CAPT ELECTED TO GET A PHONE PATCH VIA DISPATCH TO MAINT CTL. THE PATCH WAS INTERMITTENT SO ANOTHER PATCH WAS OBTAINED. AFTER PASSING ALL ENG READINGS TO MAINT CTL; THE REPLY WAS WE HAD A PRESSURE LEAK AND WOULD ONLY HAVE REDUCED PWR BUT OTHERWISE A GOOD ENG. THE CAPT DECIDED TO DIVERT AND RECONTACTED DISPATCH WITH THE RESULTS OF THE MAINT CTL COM. THE DECISION WAS TO DIVERT INTO DFW WHICH WAS ALONG OUR RTE OF FLT. ATC HANDLING WENT SMOOTHLY AND WE RECEIVED DIRECT AND OUR REQUEST FOR DSCNT TO FL240. APPROX 5 MINS AFTER LEVELING AT FL240; THE R ENG INDICATIONS RETURNED TO NORMAL AND REMAINED THERE FOR THE DURATION OF FLT. A NORMAL APCH/LNDG WAS MADE AT DFW.