LANCAIR PLT HAS AN ALTDEV DURING TRANSIT TO DEST.

Narrative

I DEPARTED IFR FROM ZZZ IN VMC WITH AN INITIAL CLRNC TO 3000 FT. ON DEP; I CONTACTED NY APCH ON 132.75 WHO CONFIRMED MY CLRNC TO 3000 FT; THEN CLRED ME TO 4000 FT A FEW MINS LATER. I SET MY AUTOPLT FOR ALT HOLD AT 4000 FT AND THE ACFT CLBED TO 4000 FT. SHORTLY THEREAFTER I WAS CLRED DIRECT WEARD AND I COUPLED MY AUTOPLT FOR GPSS TO WEARD WHICH HAD PREVIOUSLY BEEN PROGRAMMED INTO MY CHELTON FLT SYS EFIS. THE ACFT TURNED R TOWARD WEARD BUT INSTEAD OF ROLLING OUT ON THE CORRECT HDG; IT CONTINUED TO TURN. FEARING AN AUTOPLT MALFUNCTION; I DISCONNECTED THE AUTOPLT AND BEGAN TO FLY MANUALLY TO WEARD. ABOUT THE SAME TIME; I LEARNED OF TFC TO MY R (I AM NOT SURE IF I HEARD IT FROM ATC OR FROM THE 'TIS' ON MY GARMIN GTX330 MODE S XPONDER). I BEGAN LOOKING FOR THE TFC VISUALLY WHILE RESETTING MY AUTOPLT FOR ALT HOLD AT 4000 FT. AT ALMOST THE SAME TIME; THE CTLR ANGRILY SAID I WAS ABOVE MY ASSIGNED ALT OF 4000 FT. MY ALTIMETER SAID 4400 FT. I MANUALLY FLEW DOWN TO 4000 FT AND SPOTTED THE TFC ABOVE ME AND TO THE N. I KEPT VISUAL CONTACT WITH THE TFC AND CONTINUED RESETTING MY AUTOPLT FOR ALT HOLD AT 4000 FT AND A HDG DIRECT TO WEARD. UNFORTUNATELY DURING THIS PROCESS; I AGAIN CLBED TO APPROX 4400 FT AND THE CTLR ANGRILY TOLD ME TO GET BACK DOWN TO 4000 FT. AT THAT POINT I DISCONNECTED THE AUTOPLT; MANUALLY FLEW BACK DOWN TO 4000 FT AND FLEW MANUALLY UNTIL I RECEIVED A CLRNC TO A HIGHER ALT. I TOLD ATC THAT I WAS HAVING TROUBLE WITH MY AUTOPLT. AN HR LATER I WAS ADVISED BY ATC TO PHONE NY TRACON. WHEN I CALLED THEM; I WAS ADVISED THAT THEY HAD FILED A PLTDEV DESCRIBING THE ABOVE SITUATION. I SUBSEQUENTLY DISCOVERED THAT THE ORIGIN OF MY AUTOPLT PROB WAS THAT I HAD OMITTED TO SET THE COURSE TO WEARD AS DIRECT AND THE AUTOPLT WAS FLYING BACK TO THE COURSE LINE BTWN MY DEP POU AND WEARD. I SHOULD HAVE KEPT THE AUTOPLT IN ALT HOLD MODE AND RESET THE TRACK TO WEARD.