A NEW MOONEY ACCLAIM M20TN ACFT WITH S-TEC MODEL 55X AUTOPILOT COMPUTER EXPERIENCED UNCOMMANDED ALTITUDE CLIMB AND STEEP DIVE DURING TKOF CLIMB AND WINGS ROCKING DURING LEVEL CRUISE.

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I DEPARTED ZZZ IN NEW ACFT I JUST PURCHASED. I WAS TALKING TO APCH; WHO ASSIGNED ME; 'RIGHT TURN TO 120 DEGS; CLB 2000 FT.' MOMENTS LATER AN ADDITIONAL VECTOR; 'RIGHT TURN 270 DEGS.' THIS WAS A 150 DEG TURN; WHICH I THINK CAUSED THE AUTOPLT TO MALFUNCTION. THE AUTOPLT; AN S-TEC 55X; DID NOT STOP AT THE ALT PRE-SELECT ALT SETTING OF 2000 FT BUT RATHER CLBED TO 2900 FT. AT THIS POINT; THE AUTOPLT SEEMED TO REGISTER THE ALT; AND SUBSEQUENTLY PUT THE PLANE INTO A STEEP DIVE. I IMMEDIATELY DISCONNECTED THE AUTOPLT AND CORRECTED THE ALT WITH NO DELAY. ONE PROB THAT STANDS OUT IS THAT WHEN TURNING TO 270 DEGS; WHICH WAS THE 150 DEG TURN; THE AUTOPLT PUT THE PLANE INTO A BANK; MUCH STEEPER THAN USUALLY EXPERIENCED; AND SEEMINGLY DELAYING THE ALT PRE-SELECT SETTING. LATER IN THE FLT WHILE IN LEVEL CRUISE; THE AUTOPLT SEEMED TO CONSTANTLY ROCK THE WINGS. I SUBSEQUENTLY CHECKED WITH SOMEONE WHO HAS FLOWN THE PLANE AND THEY HAD THE SAME PROB.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED HE RECENTLY PURCHASED HIS NEW MOONEY 'ACCLAIM;' AND INSTALLED THE S-TEC 55X AUTOPLT BECAUSE THE G-1000 GARMIN PANEL; WHICH INCORPORATES THE GARMIN GFC -700 AUTOPILOT SYSTEM WITH A NEW MULTI-FUNCTIONAL DISPLAY UNIT; WAS NOT CERTIFIED FOR THE MOONEY 'ACCLAIM' AT THE TIME. REPORTER ALSO STATED; AS A RESULT OF HIS EXPERIENCE WITH THE S-TEC 55X AND A RECENT PREVIOUS USER OF HIS ACFT HAVING THE SAME EXPERIENCE; HE IS REPLACING THE S-TEC 55X WITH THE NOW AVAILABLE GARMIN 1000 (GFC700).