CONFUSION OVER HEADING AND ALT ASSIGNMENTS CAUSED CREW TO LEVELOFF 1000 FT HIGH.

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DURING FLT SEGMENT FROM LGA TO PBI; WHILE UNDER CTL OF ZNY WE DEVIATED FROM ALT BY ROUGHLY 1500 FT. DURING CLBOUT VECTORS WE WERE GIVEN AND READ BACK A CLRNC WE UNDERSTOOD TO BE 'TURN TO HEADING 170 DEGS; CLB AND MAINTAIN FL180.' BOTH PLTS VERIFIED THAT WE HAD PUT THE CORRECT NUMBERS IN THE CORRECT WINDOWS AND PROCEEDED TO FLY AS PROGRAMMED. WHILE EXECUTING CLRNC WE WERE GIVEN A FREQ CHANGE; WHICH ALSO INCLUDED SEVERAL 8'S AND 7'S. AFTER WAITING FOR A BREAK TO CHK IN WE CALLED IN OUT OF 17500 FT FOR FL180. WRONG FREQ. BACK TO OLD FREQ; BACK TO NEW FREQ. WE HAD ALREADY RESET ALTIMETERS IN PREPARATION FOR LEVELOFF. CURRENT ALTIMETER WAS 30.46 SO RESETTING ADDED ROUGHLY 500 FT TO OUR OFF ALT SIT. CHKED IN AND WERE TOLD WE HAD BEEN CLRED TO HEADING 180 DEGS; AND 17000 FT. WENT BACK DOWN AND WERE TOLD 'NO PROB' BY CTLR. PROB AROSE BECAUSE OF QUICK INSTRUCTIONS AND INTERCHANGEABLE ALTS AND HEADINGS. CONTRIBUTING FACTORS WERE AN XA15 WAKE UP; AND END OF THE DAY FATIGUE; AND NORMAL NYC FREQ CONGESTION PREVENTING US FROM A TIMELY CHK-IN.