MLG ENTERS LOW SPD BUFFET AS IT REACHES CRUISE ALT AND MUST DSND WITHOUT A CLRNC.

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NORMAL CLB TO 35000 FT WITH LAST 1000 FT AT 500 FPM. SPD FELL ABOUT 10 KTS BELOW OPTIMUM CLB (.72) DURING LAST 500 FT OF CLB. AFTER LEVEL OFF SPD CONTINUED TO FALL OFF AT ABOUT 2 KTS PER SECOND TO SLIGHT BUFFET AT 215 KTS. I DISCONNECTED THE AUTOPLT AND HAD TO DSND AT ABOUT 500 FPM TO KEEP THE ACFT OUT OF LOW SPD BUFFET. WE HAD VERIFIED CORRECT CLB PWR AND CHKED MAX CONTINUOUS PWR (ONLY .01 HIGHER THAN CLB) AND REQUESTED IMMEDIATE DSCNT FROM ATC WHEN AIRSPD DID NOT ACCELERATE AT LEVEL OFF. ATC GAVE US A BLOCK ALT OF 330 TO 350 AS WE DSNDED OUT OF 34600. NO CONFLICT OCCURRED. I HAD BEEN CAREFUL TO CHK OUR COMPUTER FLT PLAN TO SHOW AN INITIAL CLB TO 350 WAS OK. WE SHOWED TO BE 2000 POUNDS LIGHTER THAN PLANNED ON OUR WT DATA. ALSO OUR BUFFET CHART SHOWED WE HAD 1.3 PROTECTION AT 115000 AND WE WEIGHED 108000. ALSO THE ACTUAL TEMP AGREED WITH THE FLT PLAN. I REQUESTED A LOAD CHK AND WAS ADVISED WE WERE LOADED NOSE HVY (WITHIN 1/2 UNIT OF FORWARD LIMIT) BUT LEGAL. MY REQUEST FOR A BAG COUNT WAS REFUSED BY THE COMPANY. I CAN ONLY ASSUME WE WEIGHED MORE THAN ADVERTISED.