THE L30 DEP CTLR INFORMED THE B727-200 CREW THAT THEY MISSED THEIR TURN ON THE HOOVER 2 SID. ON TAXI OUT; THE GND CTLR CHANGED DEP CLRNC AND SAID; 'DISREGARD THE TURN.'

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TKOF WAS UNEVENTFUL. AT 6 DME; FLYING RWY HDG; PASSING APPROX 4500 FT MSL; DEP TOLD US TO 'TURN HDG 190 DEGS; YOU MISSED YOUR TURN.' WE IMMEDIATELY BEGAN AND COMPLETED THE TURN WITHOUT INCIDENT. WE RESPONDED THAT OUR CLRNC WAS TO FLY THE DEP HDG. TRACON RESPONDED; 'SORRY ABOUT THAT. WE'VE HAD SOME PROBS WITH THE TWR.' A FEW MINS LATER HE CAME BACK AND ASKED THE CAPT TO CALL THE LAS TRACON UPON LNDG AND SAID; 'NO ONE'S IN ANY TROUBLE.' I DID CALL UPON LNDG AND EXPLAINED THE SIT. THE TRACON MGR WAS INTERESTED IN WHAT HAPPENED FROM THE CREW'S PERSPECTIVE AND WHAT CLRNC WE HAD RECEIVED FROM THE GND CTL. HE DID NOT YET HAVE TIME TO REVIEW THE TAPES. HIS CONCERN STEMMED FROM THE RISING TERRAIN TO THE W OF LAS VEGAS (OUR DIRECTION OF FLT). I TOLD HIM AT THE TIME WE HAD OUR TERRAIN DISPLAY UP; WERE DOING AN 'A' PROFILE DEP AND NEVER APCHED LESS THAN 2000 FT VERTLY FROM THE TERRAIN. HE SAID THANK YOU AND HE'D BE IN TOUCH IF MORE INFO WERE NEEDED. UPON TAXI OUT FROM LAS; ATIS CHANGED WHICH RESULTED IN A SUDDEN; UNEXPECTED RWY CHANGE. THE WINDS HAD BEEN BLOWING STRONG AND GUSTY WITH WINDSHEAR MENTIONED IN THE EARLIER ATIS. THE NEW ATIS OMITTED THE MENTION OF WINDSHEAR AND CALLED THE WINDS VARIABLE AT 4 KTS. GND CTL CALLED US AND; WITHOUT PREAMBLE; BEGAN TO ISSUE A NEW CLRNC. THE FO WAS IN THE PROCESS OF WRITING IT ALL DOWN WHEN THE TWR REISSUED THE CLRNC AGAIN AND THIS TIME THE FO HAD TIME TO READ IT BACK. THE CLRNC COPIED BY BOTH CAPT AND FO; AND THE CLRNC READ BACK BY THE FO WERE ALL THE SAME: 'ACR X IS CLRED THE HOOVER 2; DISREGARD THE TURN; PEACH SPRINGS TRANSITION; J72; GALLUP; AS FILED. DEP FREQ 125.9; MAINTAIN 7000 FT.' DUE TO THE FACT THAT THE ACFT WAS VERY NEAR LEGAL MAX TKOF GROSS WT; THE SO HAD TO USE ALL OF HIS TECHNIQUES TO MAKE THE TKOF WORK WITHOUT REDUCING GROSS WT. HE HAD TO USE PACKS OFF; NONSTANDARD FLAPS; NONSTANDARD FLAP RETRACTION ALT. THE TEMP WAS HOT; DENSITY ALT HIGH AND THE RWY ASSIGNMENT WAS CHANGED FROM RWY 1R TO RWY 25R AT THE LAST SECOND. THE RESULTING SHORT TAXI MADE EVERYTHING FOR HIM EXTREMELY RUSHED. ADDED TO THAT WAS THE PRESSURE OF HOLDING UP ACR Y; AND ACR Z PARKED IMMEDIATELY BEHIND US. I MADE THE DECISION TO FORGO THE CLRNC TO 'TAXI INTO POS AND HOLD' AND HAVE THE FO INFORM THE TWR WE WEREN'T READY FOR TKOF. I DELIBERATELY CHOSE TO STOP THE ACFT AND ALLOW ACR Y AND ACR Z TO TAKE OFF AHEAD OF US. WE STOPPED THE ACFT AND DELAYED TKOF TO RE-RUN THE CHKLISTS; COMPLETE ALL BRIEFINGS OVER AND DOUBLECHK THE TKOF DATA. WE BRIEFED A FLAPS 5 DEG; PACKS OFF; PROFILE A TKOF. WE DISCUSSED WHY WE BELIEVED WE WERE TOLD TO 'DISREGARD THE TURN.' WE BELIEVED IT HAD TO DO WITH THE HOOVER 2 CAUSING A TFC CONFLICT WHILE USING BOTH RWYS (25R AND 19L) FOR SIMULTANEOUS DEPS; WHICH WAS IN EFFECT AT THAT TIME. AFTER REVIEWING THE SCHEMATIC; WE DETERMINED THAT THE 190 DEG HDG OFF OF RWY 25R WOULD CAUSE A CONFLICT S OF THE ARPT WITH DEPS COMING OFF OF RWY 19L. WE BELIEVED THAT WAS THE REASON FOR US BEING TOLD TO 'DISREGARD THE TURN.' BY US HOLDING THE 255 DEG HDG; WE WOULD REMAIN AWAY FROM ANY CONFLICT. WE DISCUSSED THAT WE FELT DEP WOULD CALL OUR TURN WHEN TFC WOULD NO LONGER BE AN ISSUE. WE THEN RAN THE BEFORE TKOF CHKLIST AND INFORMED TWR WE WERE 'NOW READY TO GO.'