B767-400 FLT CREW HAS AN ALT AND HDG DEV DURING CLB.

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WE WERE GIVEN CLRNC TO CLB TO FL190 AND HDG 340 DEGS. CLBING THROUGH 17500 FT AT APPROX 320 KTS. WE BEGAN TO EXPERIENCE MODERATE TO SEVERE TURB. TO ALLEVIATE THE EFFECTS OF THE TURB; A SPD OF 250 KTS WAS SELECTED ON THE AUTOPLT MCP. THE AUTOPLT RAISED THE NOSE TO DECELERATE AND CAUSED A VERY HIGH CLB RATE. AS WE PASSED APPROX FL185 THE AUTOPLT WENT INTO THE 'ALT CAPTURE' MODE AND WE EXPERIENCED SEVERE TYPE TURB WITH A TREMENDOUS UPDRAFT. THE HIGH CLB RATE AND UPDRAFT CAUSED THE AUTOPLT TO BE UNABLE TO CAPTURE THE ASSIGNED ALT OF FL190. ONCE I RECOGNIZED THE AUTOPLT WAS NOT GOING TO CAPTURE FL190; I DISCONNECTED THE AUTOPLT AND MANUALLY ATTEMPTED THE LEVELOFF. IT TOOK A TREMENDOUS AMOUNT OF FORWARD STICK FORCE TO STOP THE CLB AND WAS VERY DIFFICULT TO COUNTER THE UPDRAFT. THE ACFT CLBED APPROX 600 FT ABOVE FL190 BEFORE I COULD COUNTER THE UPDRAFT AND CLB RATE. AT FIRST; IT FELT LIKE MY CTL INPUTS HAD NO EFFECT. ONCE I FELT THE CTLS WERE EFFECTIVE; I RETURNED TO THE ASSIGNED ALT OF FL190. THE WHOLE EVENT WAS RESOLVED IN APPROX 10 SECONDS. DUE TO THE STRUGGLE WITH THE TURB AND ALT OUR TURN TO HDG 340 DEGS WAS DELAYED. WE FIRST NEEDED TO JUST GET CTL OF THE AIRPLANE. THE CTLR QUERIED OUR ALT AND HDG AT WHICH TIME WE WERE AT FL190-FL191 ON HDG 360 DEGS. HE THEN GAVE A VECTOR TO 330 DEGS WITH NO FURTHER COMMENT.