DEV FROM CLRNC RTE -- AN OFF COURSE AND OFF FREQ ACR CAUSES THE CTLRS TO HAVE TO MANEUVER IT TO AVOID A POTENTIAL CONFLICT.

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APCHING THE TBC VOR; THE CAPT WAS FLYING. ZDV ISSUED A FREQ CHANGE TO LAX PERCEIVED BY ALL AS 128.37. I (FO); WAS ON THE PA POINTING OUT THE GRAND CANYON AND THE CAPT MADE THE FREQ CHANGE. WE COULD HEAR ATTEMPTS TO MAKE CONTACT WITH ZLA BY THE ACFT AS WELL AS OURSELVES; BUT DIDN'T HEAR LAX RESPOND. I ASSUMED LAX WAS ON THE 'LAND LINE' OR USING ANOTHER FREQ AT THE MOMENT AND TOO BUSY TO RESPOND. AT THIS TIME THE CAPT WAS SLIGHTLY OFF COURSE TO THE L AND STARTED A TURN TO THE R. I HAD COMPLETED MY PA ANNOUNCEMENT AND GIVEN UP ON RECEIVING LAX ON 128.37 AND THUS RETURNED TO DEN ON (I THINK 127.35) ASKING FOR A REPEAT OF THE FREQ. I WAS GIVEN 128.07 AND UPON CHANGEOVER WAS CALLED BY ZLA THE SECOND I TUNED IN. THEY THEN ASKED US TO TURN L AND DSND TO FL330. WE COMPLIED QUICKLY AND SHORTLY THEREAFTER GIVEN INSTRUCTIONS TO TURN R TO 270 DEGS AND CLB AGAIN TO FL350. AS WE MADE THE FIRST TURN TO THE L WE COULD SEE ANOTHER ACFT OFF TO OUR R AT A PRETTY GOOD DISTANCE AWAY (ESTIMATED AT 3-4 MI PLUS). LAX THEN ASKED US TO CALL THE CTR UPON LNDG TO DISCUSS A POSSIBLE PLT DEV. ZLA ASKED THE OTHER ACFT IF THEY HAD A TCASII ALERT AND THEY ADVISED; NO. WE DID NOT GET A TCASII ALERT EITHER. AFTER LNDG; THE CAPT SPOKE WITH ZLA BY PHONE AND WAS ADVISED WE HAD BEEN OFF COURSE AND GETTING CLOSE TO ANOTHER ACFT. LAX ALSO SAID THEY GOT NO COMPUTER ALERT NOR DID IT PRINT AN OCCURRENCE. THE CAPT AND THE ATC SUPVR DISCUSSED THE FREQ CHANGE PROB AND THE OFF COURSE SIT; PLUS THE OTHER TFC CONVERGING AT FL350. TO PREVENT ANOTHER OCCURRENCE OF THIS TYPE SIT IN THE FUTURE I WILL INCREASE MY ALERTNESS TO WHAT IS HAPPENING WITH THE ACFT TRACKING AND HELP OR MAKE ACCURATE FREQ CHANGES AS SOON AS POSSIBLE. IF A FREQ IS IN QUESTION I WILL IMMEDIATELY MAKE A SECOND ATTEMPT IF NO CONTACT QUICKLY RETURN TO THE PREVIOUS FREQ FOR VERIFICATION. FOR ATC FREQ CHANGES; I WOULD LIKE TO SEE THEM AS FAR AWAY FROM BUSY AIRWAY INTXNS AS POSSIBLE. PA ANNOUNCEMENTS IN THE FUTURE; I WILL MAKE ONLY WHEN NOTHING ELSE IS GOING ON. I DO NOW WONDER ABOUT THE FILED COURSE CLRNCS OF BOTH OUR ACFT; AND THE OTHER OFF TO OUR R; SINCE WE WERE BOTH APCHING THE TUBA CITY VOR AT FL350. EVEN THOUGH WE WERE SLIGHTLY OFF COURSE; WAS THERE AN ALT CHANGE PLANNED FOR ONE OF US WHEN REACHING THE VICINITY OF THE TBC VOR?