@RFpilot Are you leaning the mixture at higher altitudes? At high altitudes, the mixture needs to be leaned (by pulling the red lever back) because there is less air up there. The engine will lose power if it's not leaned properly. Generally you want to aim for peak EGT (look at the EGT gauge near the throttle levers) for best economy or peak EGT + 100 degrees F for best power.