AN ACR FLC RESPONDED TO A TCASII RA WHICH OCCURRED DURING A FREQ CHANGE. THE CAPT RPTS THAT INCREASED CTLR WORKLOAD DUE TO FREQ CONGESTION AND TSTMS NEAR THE ARPT MAY HAVE CONTRIBUTED TO A LATE FREQ CHANGE AND THE RESULTING CONFLICT.

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ON CLBOUT WE NEVER RECEIVED INSTRUCTIONS TO TRANSFER FROM TWR FREQ TO DEP FREQ. I'VE NOTICED IN OPERATING OUT OF DEN; THE HDOF IS OFTEN LATER THAN WHAT I WAS ACCUSTOMED TO AT STAPLETON OR OTHER MAJOR ARPTS. THEREFORE; I WAITED UNTIL CLBING THROUGH 8000 FT MSL BEFORE ASKING THE TWR IF HE WANTED US TO SWITCH OVER. IF THERE WAS A RESPONSE; IT WAS VERY WEAK AND UNINTELLIGIBLE TO BOTH ME AND MY FO. ALSO; DURING THIS TIME; WE EXPERIENCED A ONE-TIME 'TFC' ALERT ON OUR TCASII. WE ACQUIRED THIS TARGET ABOVE US AT 11000 FT AND A COUPLE MI TO OUR 11 O'CLOCK POS. APCHING 9000 FT FOR 10000 FT I SWITCHED TO DEP TO CHK IN AFTER UNSUCCESSFULLY TRYING TO COMMUNICATE WITH TWR. UPON LEVELING AT 10000 FT; WE RECEIVED AN 'RA' ON OUR TCASII; WHICH THE FO RESPONDED TO APPROPRIATELY BY FOLLOWING THE CLB COMMAND ON OUR EADI. FOLLOWING THE RA RESULTED IN A 400 FT OVERSHOOT OF OUR INITIAL ASSIGNED ALT. WHEN CHKING IN WITH DEP; WE ADVISED THE CTLR OF OUR RA AND DEV; WHICH WAS THEN BEING CORRECTED. THE ICON REPRESENTING THE THREAT ACFT APPEARED TO CORRESPOND TO A VISUALLY ACQUIRED ACFT WELL OFF TO OUR R (APPROX 2 PLUS NM) AND APPROX 1000 FT BELOW US. WE NEVER DID FIND OUT WHETHER ATC HAD ATTEMPTED TO CONTACT US PRIOR TO OR DURING THE AURAL 'TA' AS THE TWR DIDN'T APPEAR TO BE RESPONDING TO OUR QUERY; AND DEP WAS TOO BUSY WITH OTHER ACFT AND WORKING IN A LIMITED AIRSPACE ENVIRONMENT DUE TO A TSTM N OF THE FIELD.