B757-200 DEPARTING DFW IS CHALLENGED BY ATC REGARDING ASSIGNED SPD.

Narrative

DURING CLBOUT ZFW CTLR ON 127.0 TOLD US TO MAINTAIN 300 KTS. WE ACKNOWLEDGED AND FLEW 300 KTS EXACTLY. AFTER A FEW MINS; CTLR ASKED US WHAT OUR SPD WAS. CAPT RESPONDED 300 KTS ASSIGNED. A FEW MORE MINS PASSED AND THE CTLR CALLED AGAIN AND SAID THAT WE WERE OVERTAKING ANOTHER ACFT BY 30 KTS AND THAT WE HAD INDICATED TO HIM IN OUR EARLIER CONVERSATION THAT WE WERE FLYING 305 KTS. CAPT AGAIN STATED THAT WE WERE FLYING 300 KTS AND THAT HE MUST HAVE MISUNDERSTOOD OUR EARLIER STATEMENT. I WAS FLYING THE ACFT AND HAD SELECTED THE SPD ON THE MODE CTL PANEL. THE ACFT WAS FLYING 300 KTS -- PERIOD. THE UPSET CTLR ASKED US TO SWITCH FREQ AND ASKED US TO CALL HIS SUPVR ON THE TELEPHONE ABOUT A PLT VIOLATION WHEN WE LANDED. WE CALLED AND TALKED TO HIS SUPVR ABOUT OUR SPD STATEMENT. HE SAID HE WAS JUST TRYING TO GET OUR SIDE OF THE STORY. HE SAID HE DID NOT PLAN ON FILING ANYTHING. I ASKED HIM IF HE HAD ACCESS TO THE VOICE TAPES. HE SAID HE DID. I ASKED HIM TO REVIEW THE TAPES; FOR I HAD CONFIDENCE IN WHAT WE HAD STIPULATED. I ASKED HIM TO CALL ME IF ANY PART OF MY STORY DID NOT PROVE OUT. HE SAID HE WOULD. SO FAR NO CALL.