CAPTAIN OF SA22 DECIDES TO SHUT DOWN ENGINE WHICH IS DISPLAYING APPARENTLY FALSE INSTRUMENT ANOMALIES. CONTINUES TO DESTINATION AND THEN TO AN ALTERNATE WITH EXPECTATION OF RE-STARTING ENGINE SHOULD IT BECOME NECESSARY.

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AT THE END OF THE CLBOUT; APCHING LEVELOFF FL190; I BEGAN TO GET ERRATIC ENG INDICATIONS; SPIKING EGT WITH FUEL BY-PASS LIGHT; WITH NO ACCOMPANYING PHYSICAL ENG INDICATIONS. NO SURGING; VIBRATING OR FLUCTUATING NOISE OR THRUST. I ATTEMPTED TO CTL THE SPIKING TEMP AND BYPASS LIGHT BY REDUCING THE PWR LEVER WHICH WAS SUCCESSFUL; BUT UPON ADVANCING THE PWR LEVER THE MALFUNCTION RETURNED. SINCE THE PWR LEVER HAD TO BE RETARDED TO THE POINT OF FLT IDLE TO REMOVE THE MALFUNCTION RESULTING IN OCCASIONAL NTS'ING 'NEGATIVE TORQUE SENSING;' I DECIDED A PRE-PLANNED ENG SHUTDOWN WAS THE BEST COURSE OF ACTION. I BELIEVED THAT A SINGLE REDLINE COMPUTER AND/OR A TEMP LIMITER WAS THE PROB. THE AFM ALLOWS CONTINUED FLT IN BOTH OF THESE CONDITIONS. THE DECIDED COURSE OF ACTION EXECUTED WAS A PREPLANNED SHUTDOWN WITH AN IMMEDIATE SET-UP FOR AN AIR START IN CASE OF A NEED FOR THE ENG. AFTER THE ABOVE PROCS; I INFORMED ATC THAT I WAS GOING TO REQUIRE A LOWER ALT AS SINGLE ENG PERFORMANCE WOULD NOT HOLE FL190. I INFORMED ATC I WAS NOT DECLARING AN EMER THAT I JUST NEEDED A LOWER ALT. THE RESPONSE WAS SOMETHING TO THE EFFECT OF THEY WERE GOING TO TREAT IT AS AN EMER. AFTER I WAS STABILIZED AT ALT; I ASKED ATC TO CALL DISPATCH AND INFORM THEM OF MY SITUATION. THEY CONFIRMED DISPATCH HAD BEEN NOTIFIED. APPROX 1 HR OUT OF ZZZ; I WAS ABLE TO REACH DISPATCH AND MAINT ON UNICOM. I CONFERRED WITH MAINT AS TO THE SITUATION AND POSSIBLE COURSES OF ACTION AND THE DESTS. AS I HAD OVER 3 HRS OF FUEL; I MADE AN ASR APCH AT ZZZ WITHOUT SEEING THE FIELD AND PROCEEDED TO ZZZ2 AND LANDED IN VMC.