MD80 ON CLBOUT EXPERIENCED ATC TURN TO AVOID OTHER ACFT BECAUSE OF SLOW CLB IN ZDC AIRSPACE.

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WE WERE CLRED TO CLB TO FL350; WHICH WAS THE HIGHEST THE AIRPLANE COULD CRUISE AT OUR GROSS WT. AS WE REACHED FL347; THE ACFT CLB RATE REDUCED MOMENTARILY; PERHAPS DUE TO THE ATMOSPHERIC CONDITIONS (TEMP); AND WAS STARTING TO SLOWLY CLB UP TO FL350. AT THAT TIME; THE CTLR TOLD US THAT OUR XPONDER SHOWED US 300 FT BELOW FL350; AND URGENTLY ORDERED US TO TURN 60 DEGS L OF COURSE. HE THEN TOLD ANOTHER FLT TO TURN 40 DES L OF THEIR COURSE. SHORTLY THEREAFTER; WE WERE CLRED DIRECT TO CSN; AND WE HAD ATTAINED FL350 IN THAT SHORT TIME. THE CTLR ADMONISHED US TO RPT ANY LEVELOFF IN THE FUTURE. WE DID NOT ANSWER THAT ADMONISHMENT; BUT ANOTHER PLT ON THE FREQ RESPONDED WITH A SARCASTIC 'OOOH!;' WHICH PROBABLY INCENSED THE CTLR. ALTHOUGH OUR ACFT WAS STRUGGLING TO REACH FL350; WE NEVER ACTUALLY LEVELED OFF AT FL347; AS WE CONTINUED A GRADUAL CLB UP TO FL350. THE 60 DEG L TURN DID INHIBIT OUR CLB CAPABILITY DURING THE TURN. THIS ENTIRE EVENT SURPRISED ME; AS ACFT DO SOMETIMES HAVE LOWER VERT CLB RATES AT HIGHER GROSS WTS; BUT WE NEVER LEVELED OFF AND IT WAS NOT US THAT RESPONDED SARCASTICALLY TO THE CTLR. SUPPLEMENTAL INFO FROM ACN 599004: MD88'S OPERATED NEAR THEIR MAX PERFORMANCE CEILING FREQUENTLY EXPERIENCE RAPID CLB RATES AND THEN REDUCED CLB RATES WHICH DIP UNDER 500 FPM FOR MANY SECONDS BEFORE RECOVERING. USE OF VERT SPD CAN HELP TO MAINTAIN A 500 FPM CLB RATE; BUT ELIMINATES STALL PROTECTION FOUND IN VNAV MODE. THUS; USE OF VERT SPD REQUIRES VIGILANCE ON THE PART OF CREW MEMBERS WHO USE THIS TECHNIQUE OPERATING NEAR ACFT PERFORMANCE ENVELOPES. ADVISING ATC THAT THE CLB RATE MAY ALTERNATIVELY FALL BELOW 500 FPM FOR A SHORT PERIOD BEFORE CLB RATE RECOVERY; MIGHT HELP AS AN ALTERNATIVE. WITHOUT TCASII DISPLAY OF THE OTHER ACFT AND WITH NO TFC ADVISORY FROM ATL WE HAD NO IDEA OF ANY POTENTIAL CONFLICT AND FLOWED WITH THE IDIOSYNCRATIC MD88 VNAV. AS PNF WORKING COMS WITH ATC I SHOULD PERHAPS BE MORE SPECIFIC ABOUT WHAT THE AIRPLANE IS DOING AND SEE HOW I CAN HELP ATC. ATC ASKED WHAT OUR ALT WAS FOR A REASON AND PERHAPS I APPEARED SOMEWHAT GLIB WHEN QUERIED ABOUT ALT.