FLC OF AN MD83 EXCEEDED THE ACFT PERFORMANCE LIMITATIONS AS A RESULT OF INSUFFICIENT AIRSPD AT A HIGH CRUISE ALT CAUSED BY A SLOWER CLB SPD FOR A HIGHER RATE OF CLB TO ASSIGNED ALT. THE ACFT REACTED BY STALL BUFFETING BEFORE REGAINING SUFFICIENT AIRSPD IN AN EMER DSCNT. IN ADDITION; THE ACFT'S WT AND BAL EXCEEDED CTR OF GRAVITY FORWARD LIMIT.

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DURING A NORMAL AND REGULAR FLT FROM ATL; GA; TO CANCUN; MEXICO; ON NOV/XA/98; FLYING ON AN MD-83 OF A CHARTER ACR; WE WERE CLBING TO OUR FINAL CLRED ALT OF FL330 WHEN WE RECEIVED A REQUEST FROM ATC TO REACH FL330 IN 2 MINS OR LESS. AT THAT POINT WE WERE ABOUT FL295 WITH A RATE OF CLB OF 1300 FPM TO 1500 FPM. THE SPD WE USE FOR NORMAL CLB IS 290 KTS TO APPROX FL270 AND .72 MACH FROM THERE TO WHATEVER THE CRUISE ALT WILL BE. SO WE HAD .72 MACH AT THE TIME WE RECEIVED THE REQUEST AND I INCREASED THE RATE OF CLB REDUCING THE MACH NUMBER TO MACH .70; ACQUIRING A GOOD RATE TO COMPLY WITH ATC REQUEST. WE REACHED FL330 WITH MACH .70 AND STARTED TO EXPERIENCE LIGHT AND OCCASIONAL MODERATE TURB AT THAT ALT AFFECTING CONSIDERABLY THE PERFORMANCE OF THE ACFT. FEW MINS LATER; WE WERE CLRED TO FLY DIRECT TO AN INTXN AHEAD ON THE RTE. THE TURN WORSENED THE CONDITION; MAKING IT IMPOSSIBLE TO HOLD THE AIRSPD; AND WE STARTED TO DROP DOWN FAST. AT THAT POINT WE MADE SEVERAL AND DESPERATE ATTEMPTS WITH ATC TO DSND TO A LOWER ALT; BUT UNFORTUNATELY THERE WAS TFC AFFECTING OUR DSCNT. I SAW HOW THE AIRSPD WAS DROPPING LOW AND AT THE FIRST CHANCE I ADVISED ATC THAT WE WERE UNABLE TO HOLD THE ALT AND WE WERE LEAVING FL330 TO FL280. JUST BEFORE WE STARTED THE DSCNT; THE ACFT CAME INTO ONE APCH TO STALL AND OTHER CAME ON FEW SECONDS LATER. AT THAT TIME WE WERE ALREADY DSNDING AND AIRSPD BEGAN TO RECUPERATE. WE HAD CTL OF THE AIRPLANE ALL THE TIME; BUT I THINK THAT IF WE WOULD HAVE STAYED MORE TIME AT THAT ALT A VERY BAD SIT WOULD HAVE HAPPENED. NOW I UNDERSTAND THAT I MADE A GREAT MISTAKE ACCEPTING A REQUEST THAT HAS TO BE ANSWERED IMMEDIATELY; CONSIDERING THAT WE HAVE TO CHK ON THE BEST RATE OF CLB SPD; TURB RPTS; AND MANY OTHER FACTORS INVOLVING THE SECURITY OF THE FLT THAT MAY TAKE MORE THAN 2 MINS TO CHK ON. ALSO; THE COM WITH ATC COULD HAVE BEEN MORE CLR AND PRECISE OF WHAT WAS GOING ON IN ADDITION TO THE TURB. I AM TRULY VERY CONCERNED OF WHAT HAPPENED TO ME THAT DAY AND I LEARNED THAT NO MATTER HOW PROFESSIONAL YOU ARE OR HOW EXPERIENCED YOU ARE; QUICK DECISIONS ARE NEVER EASY TO MAKE.