CAPT (PF) OVERSHOT ASSIGNED ALT WHEN HE BECAME DISTR LOOKING FOR AN INTXN LOCATION. DEP CTLR INTERVENED AND ASSIGNED HIGHER ALT.

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DEPARTED ONT AND WE WERE GIVEN A HDG TO INTERCEPT V186 IN THE VICINITY OF DARTS -- ASSIGNED ALT WAS 12000 FT. WE WERE CLBING TO THIS ALT WHEN THE HDG WAS ASSIGNED. WE INTERCEPTED THE AIRWAY AND I ASKED THE FO WHEN THE TURN WAS (AT DARTS TO V459) AND WHAT VOR FREQ I NEEDED. I KNEW WE WERE NEAR DARTS; AND THE TURN WAS COMING SOON; BUT THE FO SEEMED CONFUSED (OR POSSIBLY IT WAS TAKING TOO LONG; AND I WAS GETTING ANXIOUS); SO I LOOKED OVER AT THE CHART HE WAS HOLDING TO CLARIFY THE NAV. AT THE SAME TIME I TOOK MY ATTENTION AWAY FROM ALT (CLB RATE WAS 2000 FPM) AND CLBED THROUGH 12000 FT TO APPROX 12400 TO 12500 FT. CTLR CAME ON AND SAID CLB AND MAINTAIN 13000 FT; TO WHICH WE ACKNOWLEDGED AND LEVELED AT 13000 FT. THE MISTAKE WAS; I; AS THE PIC; ALLOWED MY ATTENTION TO BE DIVERTED FROM THE ALT AND FOCUSED ON THE NAV. IRONICALLY THE SAME THING HAPPENED ONCE BEFORE WITH THE SAME COPLT AND ALMOST THE SAME SIT. IN THE FUTURE I THINK IF THERE IS A PROB I SHOULD HAVE HIM FLY AND I'LL TAKE THE CHART.