B737 FLT CREW ENCOUNTERS TURB AND MOUNTAIN WAVE DURING CRUISE FLT AT FL410; ELECTS TO DSND TO A LOWER ALT; AIRSPD DECREASES RAPIDLY AND STALL WARNING IS ACTIVATED.

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CRUISING AT FL410; WITH CONTINUOUS LIGHT CHOP; SEATBELT SIGN WAS ON. (TURB RPTS AT ALL ALTS.) NO TP'S HAD BEEN RECENTLY ISSUED ON OUR RTE OF FLT; BUT THERE WAS TP ACTIVITY ALONG OUR RTE IN THE WX PACKET. ATC HAD BEEN QUERIED ABOUT TURB AND STATED CONTINUOUS LIGHT CHOP AHEAD. AS WE NEARED DEN; ABOUT 150 MI OR SO; OUR AIRSPD BEGAN TO INCREASE. WE PULLED THE THRUST LEVERS BACK AS THE AIRSPD CONTINUED TO INCREASE; FINALLY SETTING IN AT .85 MACH AND THE THRUST LEVERS AT IDLE. ATC INFORMED US THAT AN ACFT AHEAD OF US HAD ENCOUNTERED STRONG MOUNTAIN WAVE AND WOULD WE LIKE A LOWER ALT. WE AGREED AND WERE ASSIGNED FL390. AS WE BEGAN OUR DSCNT WE ENCOUNTERED WHAT I WILL CALL MODERATE TURB; AND INCREASED BANKING OF THE ACFT L AND R. AS I WAS TRYING TO KEEP THE ACFT WINGS LEVEL AND DSND QUICKLY OUT OF THE TURB; WE CAME OUT THE BACK SIDE OF THE MOUNTAIN WAVE. THE AIRSPD FELL OFF RAPIDLY AND I ADDED PWR. I NOTICED THAT THE AIRSPD WAS NOT RESPONDING TO THE DSCNT OR INCREASED PWR; AND WE WERE NEARING 200 KTS. MORE PWR WAS ADDED; BUT I WAS RELUCTANT TO RAISE THE NOSE AS WE WERE NEARING A STALL. THE STALL WARNING ACTUALLY WENT OFF TWICE AS WE REQUESTED A BLOCK ALT AND SETTLED AT FL370. REMAINDER OF FLT WAS UNEVENTFUL. NO INJURIES OCCURRED AS EVERYONE WAS IN THEIR SEATS.