ALTDEV ALT OVERSHOT - A TIRED FLC HEARS THE CLRNC INCORRECTLY READS IT BACK INCORRECTLY AND THEN CLBS THROUGH THE ASSIGNED ALT.

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WE DEPARTED TETERBORO ON RWY 1; CLBING OUT AS PER THE TEB 2 SID. IT HAD BEEN A LONG DAY AND WE WERE BOTH TIRED. A COLD FRONT HAD GONE THROUGH THE AREA RESULTING IN SIGNIFICANT TURB. UPON CONTACTING NEW YORK DEP; WE WERE GIVEN CLRNC TO CONTINUE THE CLB. THE FO READ BACK; 'CLRED TO 8000 FT;' AND SET THE ALT ALERTER ACCORDINGLY. I REMEMBER THINKING SUBCONSCIOUSLY THAT THE CLRNC WAS TO 6000 FT; NOT 8000 FT; BUT BECAUSE OF THE TURB; I WAS VERY TAKEN UP WITH FLYING THE AIRPLANE - THE THOUGHT WAS QUICKLY GONE. OUT OF 6800 FT; DEP CALLED SAYING; 'YOU WERE CLRED TO 6000 FT; BUT NOW MAINTAIN 8000 FT;' WHICH WE DID. I BELIEVE FACTORS IN THIS INCIDENT ARE: FATIGUE - LONG DUTY DAY. (10 HRS) - LATE IN THE DAY. (XX15 PM LCL TIME) - NUMEROUS TKOFS AND LNDGS THAT DAY. DISTRACTION: VERY UNCOMFORTABLE TURB. FAILURE OF THE CTLR TO 'HEAR BACK' PROPERLY. WE BOTH CLRLY RECALL THE FO READING BACK ALT CLRNC TO 8000 FT. THERE WAS NO CORRECTION ON THE PART OF THE CTLR. AS CREWMEMBERS; WE NEED TO BE MORE VIGILANT AND ATTENTIVE TO CLRNCS WHEN EXTERNAL CIRCUMSTANCES ARE UNAVOIDABLE. (DIFFICULT CIRCUMSTANCES). CTLRS NEED TO PAY CLOSER ATTN TO THE READDBACK.