Hi, i have 07 envoy. The truck becomes very dull/sluggish when the temperature reaches 100 degree Celsius which i believe is standard operating temperature. If the temperature is below 100 the drive is fine. No CEL. Plugs changed. Coils changed. Throttle cleaned. Solenoid cleaned. Fan clutch changed.ODO is at 250+ Kms and yes the engine was replaced with engine from similar model so i have no idea about actual mileage.