SMT OVERSHOT ALT ON CLIMBOUT DUE TO ALTIMETER PROBLEM AND HAD LESS THAN STANDARD SEPARATION WITH ANOTHER ACFT. ARTCC RADAR CTLR INTERVENED.

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DEPARTING NON RADAR FROM LAF; IN; WE WERE HANDED OFF TO ZID; 128.8; TOO LOW TO ESTABLISH RADAR CONTACT. THEN CONTACT WAS ESTABLISHED AND WE WERE TOLD TO STOP AT 5000' FOR XING TFC AT 6000'. WHILE LEVELING AT 5000' THE COPLT RPTED THE TFC IN SIGHT. THEN ATC ASKED IF WE WERE ASSIGNED 5000'. I OBSERVED BEING 5200' AND SAID WE WERE A LITTLE HIGH AND GOING BACK DOWN. I ASKED ATC HOW HIGH HE SHOWED US. HE SAID WE WERE 5700'; WHICH WAS WAY OFF OUR READING. THEN WE GOT AN ALTIMETER SETTING AND COMPARING WE FOUND THE CAPT'S READING CONSIDERABLY DIFFERENT THAN THE COPLT'S WITH MATCHED SETTINGS. MAINT FOUND ALTIMETER AND ENCODER IN ERROR. WHEN I CALLED QUALITY ASSURANCE AT ZID; THEY SAID THEY ONLY SHOWED 5500'. CONTRIBUTING FACTORS: ALTIMETER AND ENCODER FOUND IN ERROR BY MAINT. NO ALT ALERTER. NO FLT DIRECTOR. OLD ACFT; APCH 11000 HRS AIRFRAME TIME. NO AUTOPLT. WE DON'T RECALL GETTING AN ALTIMETER SETTING BECAUSE HE DIDN'T ORIGINALLY HAVE US IN RADAR CONTACT. COLD FRONT IN AREA; ATIS AND CENTER ALTIMETER SETTING MAY HAVE DIFFERED. PLT FATIGUE. A) FLEW HARD IFR ALL DAY ALONG COLD FRONT; HANDS ON; NO AUTOPLT. B) FLEW 5.3 HRS; 4 APCHS; 10 HRS DUTY. C) WE WERE BEHIND ALL DAY DUE TO ATC AND WX; AND LATER REALIZED WE HAD HAD BREAKFAST ONLY AND THAT WAS 6 HRS EARLIER. D) CAPT REACTION TIME MAY HAVE BEEN SLOWED. E) COPLT ALT CALLOUTS WERE DISTRACTED BY TFC SCAN. A GOOD NOTE; WE DID HAVE THE TFC IN SIGHT AND THERE WAS NO CONFLICT. IF 135 COMMUTER REGS WERE AS STRINGENT AS 121 REGS AND ALT ALERTERS AND AUTOPLTS WERE REQUIRED; IT MAY HAVE HELPED. I THINK 135 COMMUTER PLTS WORK HARDER BECAUSE FLT AND DUTY TIMES ARE LONGER AND WE ARE STUCK DOWN IN THE WX WHERE JETS ARE ABOVE WX AND AWAY FROM GA TFC. MY ACFT GOES 260 KTS TRUE; AND I ALWAYS SAY THE ONLY THING WE DON'T DO THAT THE JETS DO IS GO FASTER THAN 250 KTS ABOVE 10000'. OUR APCH SPDS ARE THE SAME. WE DO 8-10 LEGS A DAY AND THEY DO 6. SUPPLEMENTAL INFO FROM ACN 91344: WHILE SCANNING FOR TFC; I CALLED COMPANY OPS AT LAF AND ADVISED THEM OF OUR OUT AND OFF TIMES. AT THIS POINT WE WERE PASSING THROUGH APPROX 3200' MSL. THE TFC WAS LOCATED AND CALLED AT 12:30-1 O'CLOCK; AND WE WERE LEVELING AT THIS TIME. I ACKNOWLEDGED THAT WE WERE TOLD TO STOP AT 5000' AND AT THIS TIME MY CAPT TOOK OVER RADIO COMS WITH ZID. HE MADE COMMENT THAT WE WERE A LITTLE HIGH AND THAT WE WERE GOING BACK DOWN TO 5000'. I LOOKED DOWN AT MY ALTIMETER AND AT THAT TIME WE WERE PASSING THROUGH 5200' MSL. WE RETURNED TO 5000' ASSIGNED ALT AND COMPARED ALTIMETERS. THE CAPT'S ALTIMETER WAS FOUND TO BE READING HIGHER THAN THE COPLT'S AND UPON ARR AT DAY WE ASKED OUR MAINT PERSONNEL TO INSPECT THE ACFT FOR ALTIMETER PROBS AND A NUMBER OF OTHER PROBS. OUR MECH TOLD US THAT THE CAPT'S ALTIMETER WAS INDEED IN ERROR.