WHILE TRACKING THE DGW 340 DEG RADIAL; LTT CREW ARE TOLD THEY ARE 5 MI E OF COURSE.

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DEPARTED GILLETTE; WY. WE WERE FILED V254 TO DGW ON OUR WAY TO DEN. APPROX 50 MI FROM GCC (HALF WAY BTWN THE VORS) WE SWITCHED BOTH VOR RECEIVERS TO DGW. BOTH HSI'S INDICATED WE NEEDED ABOUT 1/2 DOT CORRECTION TO THE L. THE FO WAS FLYING; AND HE CORRECTED A COUPLE OF DEGS L UNTIL THE HSI NEEDLE WAS CTRED. ABOUT 8 OR 10 MINS LATER; THE CTR CTLR ASKED IF WE WERE FILED V254. WE REPLIED THAT YES; WE WERE. HE THEN TOLD US WE WERE 5 MI L OF THE CTRLINE. SINCE BOTH OUR HSI NEEDLES WERE CTRED; WE CHKED OUR CHART TO MAKE SURE WE HAD THE RIGHT RADIAL. WE DID. WE ASKED THE CTLR TO CONFIRM THAT WE SHOULD BE TRACKING THE 340 DEG RADIAL TO DGW. HE DID NOT ANSWER. FINALLY; WE TOLD HIM THAT WE SHOWED ON COURSE. HE CAME BACK; SOUNDING IRRITATED; AND TOLD US TO TURN 15 DEGS R AND HE WOULD TELL US WHEN WE WERE BACK ON COURSE. WE COMPLIED. WE THEN SWITCHED BOTH RADIOS BACK TO GCC. WE WERE NOW 85-90 MI FROM GCC. THE RADIOS NOW SHOWED ABOUT 10 DEGS DIFFERENCE BTWN GCC AND DGW. WE NOTIFIED THE CTR CTLR OF THIS FACT; BUT HE WOULD NOT ACKNOWLEDGE OUR XMISSIONS. AFTER RETURNING TO DEN; 2 OF OUR OTHER CAPTS WHO HAD HEARD THE EXCHANGE ON THE RADIO TOLD US THEY HAD HAD A LOT OF PROBS WITH DGW RADIALS 'WANDERING' AND WERE GOING TO ASK FOR ALTERNATE NAVAIDS TO AND FROM GILLETTE IN THE FUTURE. I BELIEVE THAT THE DGW VOR SHOULD BE CHKED FOR RELIABILITY.