AN MD11 CREW RECEIVED A LATE DSCNT CLRNC FROM THEIR CRUISE ALT. THE AUTOPLT CAPTURED A FALSE GS WHICH RESULTED IN A HIGH APCH AND SUBSEQUENT GAR. CONFUSION ABOUT HDGS DURING THE GAR VECTOR CONTRIBUTED TO THE RPTR DEVIATING FROM HIS ASSIGNED ALT BY 500 FT.

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FOLLOWING AN INTERCEPT OF THE LOC; A GS WAS INTERCEPTED; BUT WHEN WE VISUALLY ACQUIRED THE FIELD; WE WERE OBVIOUSLY TOO HIGH AND WOULD REQUIRE A GAR. APPARENTLY THE AUTOPLT INTERCEPTED AND DISPLAYED A FALSE GS. WE WERE ISSUED A NON-STANDARD GA (STANDARD WAS 3000 FT TO A FIX WITH L TURN TO INTERCEPT AN OUTBOUND RADIAL). THE ISSUED GA WAS TO 5000 FT AND A TURN TO A HDG. WHETHER THIS WAS A VECTOR TO DOWNWIND OR A VECTOR TO INTERCEPT PUBLISHED RADIAL WAS UNCLR. DURING THE GA; THE 5000 FT LIMITATION WAS VIOLATED. I NOTED 5500 FT TWICE DURING MANEUVERING. WHILE WE WERE MANEUVERING TO INTERCEPT PUBLISHED OUTBOUND MISSED APCH RADIAL; APCH CTL FINALLY MADE IT CLR WE WERE ON VECTORS FOR ANOTHER APCH TO THE RWY. VECTORS BACK TO THE FINAL APCH COURSE AND NORMAL LNDG WAS THEN ACCOMPLISHED. THE PROB STARTED BECAUSE WE COULD NOT START A DSCNT WHEN REQUIRED. A SECOND PROB WAS THE REQUEST TO GO-DOWN AND SLOW-DOWN AT THE SAME TIME; A DIFFICULT THING TO DO IN A LARGE ACFT. THE THIRD PROB WAS THE UNANTICIPATED NON-STANDARD GA; WITH CONFUSING INSTRUCTIONS AS TO THE REQUIRED HDG (IS THIS A VECTOR TO SOMEPLACE OR A VECTOR TO INTERCEPT PUBLISHED OUTBOUND RADIAL?). ATC'S CONTRIBUTION TO THE DEVELOPING PROB WAS THE ISSUANCE OF INCORRECT OR INAPPROPRIATE FREQS TO ESTABLISH A DSCNT; BUT AS A PLT; I SHOULD HAVE REFUSED ATC'S REQUEST TO CORRECT THE PROB WITH SPD AND HIGH RATES OF DSCNTS. SUCH MANEUVERS DO NOT WORK WELL; ESPECIALLY IN AN FMS ACFT. A NON-STANDARD GA ALSO BECAME A PROB BECAUSE FMS PROGRAMMED PARAMETERS INTERFERED WITH THE VERBAL INSTRUCTIONS. HAVING NEVER BEEN TO ZZZZ BEFORE AND BEING UNFAMILIAR WITH THE SPECIFIC APCH ALSO CONTRIBUTED TO THE DIFFICULTIES.