What was found
FLIGHT DEPARTED, TAKEOFF WAS STANDARD WITH NO ABNORMALITIES NOTED. CLEARED TO FL 280, WHEN LEAVING 12,000 FEET, THE PILOT BELIEVED THERE WAS A DECREASE IN CLIMB PERFORMANCE. THE LEFT ENGINE ITT WAS FLUCTUATING BETWEEN 700 AND 830 DEGREES WITHOUT THRUST LEVER INPUT, AND LATER STABILIZED AT 810 DEGREES. AFTER TEMPERATURE STABILIZATION AT 810 DEGREES, POWER COULD NOT BE INCREASED TO GET THE PERFORMANCE NEEDED FOR A NORMAL CLIMB, EVEN WHEN THE THRUST LEVER WAS POSITIONED TO MAXIMUM POWER. MOREOVER, THE RIGHT ENGINE WAS NOT PRODUCING THE MAX POWER NEEDED AND TEMPERATURE WAS NOTED AS 820 DEGREES WITH THE THRUST LEVER AT MAXIMUM POWER SETTING. AFTER REVIEWING THE QRH AND COMPLETING ALL CHECKLISTS, RETURNED TO DEPARTURE. CHECKLISTS WERE COVERED AND LANDING WAS COMPLETE WITHOUT ANY FURTHER ISSUES.