DEPARTING MDSD; B757-200 FLT CREW RECEIVES CONFUSING CLRNC WHICH RESULTS IN DISAGREEMENTS WITH ATC REGARDING THEIR RTE OF FLT AND ALT.

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DURING TAXI OUT; FO COPIED AND READ BACK CLRNC AS DIRECT PITOX; MAINTAIN 3000 FT. AFTER TKOF ON RWY 17; ON FIRST CONTACT WITH LAS AMERICAS DEP WE WERE GIVEN CLRNC TO 15000 FT. AT APPROX 1500 FT FO BEGAN A L TURN TO PITOX. AT 2700 FT DEP TOLD US WE WERE CLRED TO PITOX AT 3000 FT. FO BEGAN A QUICK LEVELOFF; BUT DEP THEN RECLRED US DIRECT TO PTA TO MAINTAIN 15000 FT. HE ALSO INFORMED US THAT TWR HAD CLRED US VIA THE PITOX DEP TO MAINTAIN 3000 FT. THERE WAS NO FURTHER RADIO DISCUSSION OF THE SIT. AFTER REVIEWING THE SID PAGES; IT APPEARS THAT THE ONLY DEP PROCS ROUTED THROUGH PITOX ARE FROM RWY 35. ADDITIONALLY; NONE OF THE SIDS ARE ACTUALLY NAMED 'PITOX DEP;' AND THE FMS DATABASE CONTAINS NO SIDS BY THAT NAME. APPARENTLY ATC WAS EXPECTING US TO FLY A DIFFERENT PROC FROM WHAT WE FLEW; BUT IN OUR OPINION WE WERE FOLLOWING THE CLRNC RECEIVED (AND READ BACK). I HAVE HAD NUMEROUS COM PROBS AND DIFFICULTIES WITH THE SDQ TWR CTLRS; AS THEY ARE OFTEN QUITE DIFFICULT TO UNDERSTAND; AND THEIR XMISSIONS ARE FREQUENTLY CHOPPY (PROBABLY DUE TO A BAD MIKE CONNECTION OR A SHORT; BUT IT SEEMS LIKE THEY JUST DON'T HOLD THE BUTTON DOWN LONG ENOUGH). I WOULD VERY MUCH LIKE TO KNOW WHAT THE PITOX DEP FROM RWY 17 CONSISTS OF; AND WHY IT IS NOT DEPICTED EITHER ON THE PAGES OR IN THE FMS DATABASE.