ATC CTLR OVERLOAD. TFC SEPARATION.

Narrative

FLT X FROM ORL TO ATL APPROX 20 DME S OF HUSKY INTXN ON SIERRA ARR PROCEEDING DIRECT TO HUSKY AT 310 KTS CTLR CLRED US TO CROSS HUSKY AT 14000 FT. WE STARTED DOWN BUT REALIZED THAT WE COULD NOT MAKE XING RESTR. THE FREQ WAS VERY CONGESTED; AND BY THE TIME WE WERE ABLE TO TELL THE CTLR THAT WE COULDN'T MAKE THE RESTR WE WERE AT 21500 FT. CTLR THEN INSTRUCTED US TO TURN TO A 90 DEG HDG WITH NO FURTHER INSTRUCTION ON ALT. WHEN WE ASKED WHAT ALT HE WANTED; HE SAID FL230. SINCE WE WERE ALREADY AT FL215 WE TOLD HIM WE WOULD LEVEL OFF AT FL210. THE FREQ AT THE TIME WAS VERY CONGESTED; AND IT SOUNDED AS THOUGH THE CTLR WAS REACHING THE POINT OF OVERLOAD. A PREVIOUS ACFT (POSSIBLY Y) HAD A MISCOM WITH THE CTLR WHICH RESULTED IN A SIMILAR ALT CONFUSION. AFTER OUR TURN TO 90 DEGS; AND LEVEL AT FL210; THE CTLR STARTED TO CLR AN ACFT OVERHEAD US AT FL220 DOWN TO FL210; BUT CORRECTED HIS MISTAKE IMMEDIATELY. WX IN THE AREA WAS A CONTRIBUTING FACTOR. DUE TO THE LARGE NUMBER OF ARRS; AND DETERIORATING WX CONDITIONS; THE CTLR APPEARED TO BE REACHING THE POINT OF OVERLOAD.