NUMEROUS FACTORS COME TOGETHER CAUSING ENOUGH DISTR TO RESULT IN AN ALT OVERSHOOT DEPARTING LAX.

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I WAS SEAT SWAPPING WITH THE CAPT. WE WERE 1 HR 15 MINS LATE INTO SOCAL DUE TO FOG/MARINE LAYER IN LOS ANGELES. WE HAD A SCHEDULED ACFT CHANGE AND PROCEEDED TO OUR NEW GATE WITH ME AS THE ACTING CAPT. AFTER START AND TAXI; WE WERE CHANGED TO THE S COMPLEX FOR DEP. WE REVIEWED THE LAXX 3 DEP AND HDG CHANGE TO 220 DEGS VERSUS 250 DEGS ON THE N DEP. AT TKOF; WE TURNED TO 220 DEG HDG AND WERE XCHKING A XING RADIAL. AT THIS TIME WE WERE VECTORED TOWARD THE S VIA A 160 DEG HDG AND THEN A 120 DEG HDG. AT THIS TIME WE PASSED 3000 FT MSL AND NOTICED 4000 FT IN THE ALT WINDOW. WE LEVELED AT 3400-3500 FT AND STARTED DOWN TO 3000 FT AND TRIED TO CONFIRM OUR CORRECT ALT WITH SOCAL DEP. WE BOTH COULDN'T REMEMBER THE CHANGE IN ALT CLRNC. WHEN WE FINALLY TALKED TO SOCAL TO VERIFY; HE ANSWERED 'CLB NOW TO 6000 FT' AND NEVER CONFIRMED OUR LAST CLRNC ALT. CONTRIBUTING FACTORS: LATE. PLANE CHANGE. DEP DIFFERENT THAN EXPECTED. SEAT SWAP -- EVERYONE CONCENTRATING ON NEW DUTIES. BUSY RADIO FREQ WITH NUMEROUS FLT PATH CHANGES.