A B737-300 IN CLB AT FL290 TO LEVEL OFF AT FL330. CAPT'S AND FO'S ALTIMETERS AND AIRSPD INDICATORS IN DISAGREEMENT; EXCEEDING ALLOWABLE LIMITS. RETURN LAND AT DEP ARPT.

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DEPARTED ZZZ FOR ZZZ1. ALL PREFLT INDICATIONS WERE NORMAL. CAPT AND FO AIRSPD CHKED IN AGREEMENT AT 80 KTS AND V1. 29.92 WAS SET AT TRANSITION ALT FL180. AT FL290; CREW NOTICED DISAGREEMENT IN ALTIMETERS (FO HIGH APPROX 600 FT). XCHKED STANDBY ALTIMETER (WHICH AGREED WITH FO ALTIMETER) AND CONFIRMED 29.92 SET BOTH SIDES. INITIAL LEVELOFF AT FL330 (ON FO SIDE); ALSO NOTICED AUTOTHROTTLE NOT KEEPING SPD. (.76 MACH SET; FO AIRSPD INDICATING .78 MACH; CAPT AIRSPD INDICATING .74 MACH). AUTOTHROTTLE OBVIOUSLY TRYING TO CATCH CAPT'S SPD. NO FLAGS PRESENT. AUTOTHROTTLE TURNED OFF AND 'AIRSPD/MACH UNRELIABLE' EMER CHKLIST ACCOMPLISHED. REF ACTION STATES 'UNRELIABLE INDICATIONS WITHOUT FLAGS GENERALLY ARE CAUSED BY A PITOT STATIC SYS PROB WHICH CANNOT BE FIXED INFLT.' CALLED DISPATCH AND PHONE PATCH TO MAINT CTLR. MAINT CTLR GOT ENGINEERING OK TO ATTEMPT TO CYCLE ADC CIRCUIT BREAKERS INFLT; WHICH DID NOT HELP. WE HAD ELECTED TO DIVERT TO NEAREST SUITABLE ARPT (ZZZ2) PER FLT MANUAL GUIDANCE. 'IF INDICATIONS ARE UNRELIABLE; LAND AT NEAREST SUITABLE ARPT.' DURING DSCNT CAPT'S AIRSPD AND ALTIMETER ERRORS GRADUALLY REDUCED AND EVENTUALLY MATCHED THOSE OF FO AND STANDBY INSTS. I RECEIVED ACARS MESSAGE FROM DISPATCH SAYING FLT OPS DISPATCH RECOMMENDED LNDG ZZZ; SINCE INDICATIONS WERE NOW NORMAL. I CONSENTED AND DIVERTED BACK TO ZZZ.