PIPER ARROW IS SLOW TO CLB WHEN UNABLE TO GET CONFIRMATION OF CLRNC.

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ON IFR FLT PLAN WINSTON-SALEM; NC (INT); TO FREDERICK; MD. HAD JUST LEVELED AT 7000 FT; THE ALT FILED FOR. ZDC WAS BUSY WITH A LOT OF TFC AND ISSUED AN INSTRUCTION TO 'CLB TO 9000 FT.' BEFORE THE CLB; IT TOOK ABOUT 45 SECONDS TO GET A WORD IN ON THE FREQ TO REQUEST A CONFIRMATION THAT I FILED FOR 7000 FT; NOT 9000 FT. AT THIS POINT THE AGGRAVATED CTLR 'LECTURED' ME FOR ABOUT A MIN INDICATING I SHOULD CLB FIRST AND REQUEST CONFIRMATIONS LATER. I IMMEDIATELY COMPLIED WITH THE CLB CLRNC WHILE HE WAS 'DISCUSSING' THIS WITH ME. HE STOPPED ME AT 8000 FT AND A FEW MINS LATER RETURNED ME TO 7000 FT. HE DID NOT SAY 'IMMEDIATELY' CLB OR DID NOT EXPRESS ANY 'URGENCY' WITH THE REQUEST. I THOUGHT HE THOUGHT I FILED FOR 9000 FT SINCE HIS INSTRUCTION CAME JUST AFTER LEVELING AT 7000 FT. IF HE HAD A TFC CONFLICT WITH ME; HE DID NOT INDICATE IT TO ME. I WILL HEREAFTER COMPLY FIRST; QUESTION THE CLRNC SECOND IF NECESSARY. I FEEL THE CTLR SHOULD SEEK A CONFIRMATION OF INSTRUCTIONS; SHOULD EXPRESS ANY URGENCY BY SAYING 'CLB IMMEDIATELY;' OR BRIEFLY OFFERING ANY EXPLANATION TO THE PLT.